Category Archives: Volcanology

Today in Geological History; December 24th -Tangiwai Disaster

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The Tangiwa disaster was New Zealand’s worst rail accident, which at face value looks out of place on this site. but the incident was infact indirectly caused by the earlier eruption of Mount Ruapehu.

Mount Ruapehu sits at the southern end of the Taupo Volcanic Zone and is the largest active volcano in New Zealand. In 1945 eruptions began in March and ran intermittently through out the year. Activity varied greatly from gentle steam plumes to doming in Crater Lake.

The activity in 1945 had several dire consequences. In July geologists Robin Oliver and J. Witten Hannag has a lucky escape when an explosion showered them with hot rocks and ash leaving Oliver unconscious and seriously burnt. The heavy ashfall through out the last few months of the year also led to the closure of a hospital 9 km away from the crater as ash kept penetrating the generators. Over the year hundreds of people were diagnosed with what doctors termed ‘Ruapehu’s Throat’ where people were suffering with breathing difficulties from inhaling the dense ash. But the worst of all was the Tangiwa disaster.

The activity of 1945 carved out the crater deeper than it previously was and once activity had ceased the crater began filling with water. By 1953 the water level had risen over 8 meters higher then it was before the eruptions and was only contained by an unstable mass of ice and volcanic rubble and ash. At 8 p.m. on Christmas Eve 1953, the debris at the outlet of Crater Lake collapsed sending 340,000 cubic metres of water pouring into the head of the Whangaehu River. It swept down the valley, picking up sand, silt and boulders as it went. Soon after 10 p.m. the lahar smashed into the main trunk railway bridge at Tangiwai. The concrete piers were knocked out and the bridge partially collapsed.

A passenger train from Wellington, packed with 285 people heading to Auckland for the holidays had no idea what lay ahead as it approached the bridge in the dark. A local who saw the bridge collapse tried to flag down the speeding train but even though the driver saw him and applied the brakes the train was going to fast and still carried on to the bridge. The engine and first carriage nosedived, landing against the opposite bank. Four more carriages plunged into the river, floating in the torrent briefly before sinking. Another four carriages remained on the track, but one of them dangled over the river.

One carriage was carried more than 2 kilometres downstream. The others were swept across the flooded main road or rammed into the riverbanks. Some people had escaped and swam to the banks, but dozens drowned in the tangles of gorse there. The work of recovering victims went on for several days along 60 kilometres of the river. Twenty bodies were never found; it was assumed they had washed out to sea, some 120 kilometres away. 151 people lost there lives due events set in motion by a volcano 8 years earlier.

Figure 1. http://mp.natlib.govt.nz/detail/?id=7617&l=mi

Figure 2. https://www.flickr.com/photos/archivesnz/11440413944

 

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The New Decade Volcano List; #5 Trans Mexico Volcanic Belt

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The guys at Volcano Cafe have picked up where they left off with a rather interesting choice at number 5. Mexico is one of the more volcanically active countries in the world, with the likes of Popocatépetl and Colima frequently showing at least some signs of unrest.  This has been one of my favourites which they have put forward as it highlights the complexity of the region and how several systems can affect a region meaning threat can come from varying or even all sources!

Mexico City and the Trans Mexico Volcanic Belt – NDVP #5

The extinct volcano Sierra de Guadalupe rises 750 metres above Mexico City, it’s highest peak within 15 km of the centre of the city. In spite of conservation attemps, illegal buildings continue to sprout and at present the crater and debris avalanche have been completely covered by urban development. (Hotu Matua)

It is inevitable that the higher we get in this series, the more speculative our choices may seem. If everything was known about every volcano, identifying and motivating the choice of the ten most dangerous ones would be a relatively simple matter. As it is, our selections have to be based on what meagre information is available and educated guesswork as to what the full story might or could be. In our choice of number five, this is highlighted as we cannot even identify a single volcanic system as the main threat, but then the area occupied by the cities Mexico City, Toluca and Puebla is highly unusual.

Throughout almost its entire length, the Ring of Fire produces volcanoes aligned on and along the subduction zone forming a great arc of stratovolcanoes which has given rise to the term “Arc Volcanism”. But running across Mexico from Colima in the west to Pico de Orizaba in the east, the subduction zone makes an almost 90-degree turn and the volcanoes seem to align on a N-S line, perpendicular to the subducting plate. Three main such alignments are identified in recent scientific papers; Cántaro–Nevado de Colima–Colima de Fuego in the west, Tláloc–Telapón–Iztaccíhuatl–Popocatépetl (Sierra de Nevada) just east of Mexico City, and Cofre de Perote–Las Cumbres–Pico de Orizaba–Sierra Negra at the eastern end of the Trans Mexico Volcanic Belt, alternately known as the Trans Mexico Volcanic Zone. For the entire TMVB, volcanism has trended from acidic (dacite and rhyolite) to intermediate magmas (andesitic) as well as from north to south although there are numerous and noticeable exceptions to these identified trends.

The geological setting of the Trans Mexico Volcanic Belt. The numbers next to the arrows showing the direction are the annual subduction rates. The numbers along the isolines display the depth of the subducting plate as inferred from earthquakes. The TVMB is outlined in grey and the alignment of volcanoes mentioned are in yellow. Note how volcanoes (north-)west and (south-)east of the TMVB seem to align along the 300 and 100 km subduction isolines as opposed to transversing them as is the case in the TMVB. (Adapted from Macías 2007)

In addition to these three main lines of active volcanism, there are further lines of dormant or extinct volcanoes, one bordering the Mexico City plain to the west and the Toluca plain to the east with another one bordering the latter plain to the west. To complicate the matter even further, both north and south of these plains run lines of ancient, heavily eroded and extinct(?) volcanic edifices that seem to follow the subduction zone. If we also include the Puebla plain to the east of the Sierra de Nevado, there are more than 1.6 million inhabitants of Greater Toluca, 22.5 million of Greater Mexico City and 2.1 million of Greater Puebla, in all well in excess of 25 million.

Landsat image of the Toluca, Mexico City and Publa plains. The names of active to potentially active volcanoes in yellow, possible volcanic alignments are marked in blue and the 90-km-long Chichinautzin volcanic field immediately south of Mexico City, centred on the Aztec temple El Tepozteco, is circled. (Author)

Not only is the north-south alignment perpendicular to the subduction zone of the most recent volcanoes highly unusual. There is as well a dearth of large, explosive calderas in the TMVB. The semi-official blog GeoMexico laments: “There is still lots of work needed to fully unravel the geological secrets of Mexico’s Volcanic Axis which crosses the country between latitudes 19 and 21 degrees North. Unlike most volcanic belts elsewhere in the world, this one does not appear at first sight to correspond to any plate boundary. Another of the mysteries of this volcanic region, where igneous upheavals have shaped the landscape for several million years, is the relative dearth of calderas, the “super craters” formed either by collapse or by giant explosions.”

As of 1999, there were seven calderas known in the belt, one of which is in fact no more than a crater lake, Lake Alchichica, with a diameter of 1888 meters. The largest of these seven calderas is the 15 by 21 km Los Humeros caldera in the state of Puebla, close to its border with Veracruz. It lies 55 km west-north-west of the city of Veracruz (Xalapa), relatively close to Puebla (Teziutlán). The main caldera is about 400 m deep and roughly oval in shape. Prior to its formation 460,000 years ago, lava emitted from this vent covered 3500 square km with ignimbrites. Later, two smaller calderas formed nearby, with ages of about 100,000 years (Los Potreros caldera) and 30,000 years (El Xalapazco) respectively.

The 11 km wide and 400 m deep, heavily eroded Amealco caldera is located at Garabato (= unintelligible scribbles), midway between the towns of San Juan del Río and Maravatio, about 125 km NW of mexico City. Caldera-related activity started in the Pliocene ca. 4.7 Ma ago and ended around ca. 2.2 Ma. The total volume of pyroclastic flow deposits and ignimbrites is in the region of 500 cubic km. The Huichapan Caldera in the central sector of the TMVB, also referred to as the Donguinyó-Huichapan caldera complex is 10 km in diameter and appears to be the result of two overlapping calderas that date to 5 and 4.2 million years ago respectively. The rocks from the older caldera are intermediate to basic in composition, while those from the more recent caldera are acidic (high silica content) rhyolites, another relatively unusual feature.

Since then, one very interesting albeit ancient feature has been discovered in the Coxcatlán-Tilzapotla region, about 100 km south of Mexico City, just south of the TMVB. The elliptical NW-SE oriented dome structure, approximately 30 x 52 km, encompasses the Tilzapotla collapse caldera, rhyolitic domes, large volumes of ignimbrites, as well as the Buenavista intrusive body, and the Coxcatlán and Chautle plutons located west and east of the structural margin of the caldera, respectively. Previous geochronological studies carried out on the silicic and intermediate magmatic rocks places the uplift in the dome area in the late Eocene (~38-34 Ma). This suggests that doming was related to emplacement of magmas into the crust prior to collapse of the Tilzapotla caldera at 34.3 Ma.

The approximately 11 x 13 km Tilzapotla caldera is located on top of this large, rhyolitic dome feature. “The caldera is defined by a 33 x 24 km semi-elliptical structure that encircles the largest exposures of the Tilzapotla ignimbrite and corresponds to the structural margin rather than the topographic rim. A central uplifted block limited by NW-trending faults is the main indication of a resurgent stage. The caldera structural margin is surrounded by extensive exposures of Cretaceous marine sequences that structurally define a broad elliptical dome (45×35 km) originated in the first stage of the caldera evolution. There is evidence showing that the 34 Ma Tilzapotla ignimbrite represents the climatic event of the caldera collapse.” (Morán-Zenteno et al 1998) This begs the question of how the very large dome feature itself was formed. It covers some 1500 square kilometres to a height more than 1,000 m above the surrounding plains with a total thickness in excess of 800 m. If we make allowances for surface depression and 34 My of erosion, the total volume emitted is in excess of 1,500 cubic kilometres of silicic magma.

The observed absence in the TMVB of the elsewhere omnipresent large explosive calderas is a conundrum. Either they have been masked by the products of subsequent volcanic eruptions and rapid, tropical erosion and still await discovery, or, volcanism in the TMVB is sufficiently different to almost preclude these eruptions. However, the presence of the >500 km3 Amealco caldera, the 15 by 21 km Los Humeros caldera and the 10 km Huichapan Caldera rather points to the former being the case. In order to gain an insight into how very complex Mexican volcanism can be to unravel, at this point I recommend a look at the reconstruction by Diaz & McDowell (page 11); “Figure 7. Volcanic evolution of the Amealco caldera and peripheral volcanoes”. It is unfortunately too large to reproduce here, so please, take a look!

http://www.geociencias.unam.mx/~ger/2000_GSASP_334_Ame.pdf

If we turn our attention away from the very largest types of eruptions, there are several large and highly dangerous volcanoes in the Toluca – Mexico City – Puebla area. To the SW of Toluca lies the giant stratovolcano Nevado de Toluca and 50-70 km east and southeast runs the Sierra Nevada mountain range comprised of four major volcanoes:

The 4,680 m a.s.l. high Nevado de Toluca volcano as seen from the city of Toluca, 24 km away. (Wikimedia Commons)

Nevado de Toluca

In the Nahuatl language, “Xinantécatl” means “naked man”. Alternately, the name has been interpretated as “Chicnauhtécatl”, “nine hills” which given the volcano’s appearance seems the likelier. Nevado de Toluca is a composite volcano of late Pleistocene-Holocene age with a calc-alkaline andesitic to dacitic composition. The northern flank of Nevado de Toluca has a relative elevation (prominence) of 2015 m with respect to the Lerma river basin, and its southern flank has a relative elevation of 2900 m with respect to the Ixtapan de la Sal village. The elliptical 1.5 by 2 km wide crater of Nevado de Toluca is breached to the east. The interior holds a dacitic central dome and the remains of two ancient scars, located on the SE and NE flanks of the volcano which are related to the partial collapse of the edifice. Unusually for volcanic lakes, the two crater lakes are alkaline, not acidic.

El Refugio quarry located 15 km northeast of Nevado de Toluca crater showing an exposure of the 37,000 yr B.P. block-and-ash flow deposits (Macías 2007)

Nevado de Toluca was built upon the intersection of three fault systems with NW-SE, NE-SW, and E-W orientations. This structural geometry favoured the formation of coalescent pyroclastic fans that reach all the way to the cities of Toluca and Metepec, 25 km to the NE of the volcano. During the late Pleistocene, the southern flank of Nevado de Toluca collapsed twice, originating debris avalanche deposits that were transformed into debris flows with distance. The scars produced by these collapses have disappeared due to subsequent volcanic activity and glacial erosion. The older flow can be traced to distances up to 35 km from the summit while the younger event near the end of the Pleistocene ( > 40 kA) generated a debris avalanche, the “Pilcaya Debris Flow”, that travelled more than 55 km from the summit. Activity then continued with three very large explosive eruptions – the Lower Toluca Pumice ca. 21,700 yr B.P., the Middle Toluca Pumice ca. 12,100 yr B.P. and the Upper Toluca Pumice ca. 10,500 yr B.P. The pyroclastic deposits of these eruptions are mostly covered by subsequent and “smaller” Plinian eruptions.

The Sierra Nevada Volcanic Range

From north to south, the Sierra Nevada Volcanic Range comprises the volcanoes Tláloc, Telapón, Iztaccíhuatl, and Popocatépetl. Previously, it was considered that volcanic activity began to the north and migrated south but new evidence obtained from previous studies, field reconnaissance and radiometric dating paints a slightly different picture.

During the past 10,000 years, there have been repetitive Plinian eruptions of Popocatépetl including some historic events and the 1994–present eruption, but Holocene activity has not been limited to Popocatepetl alone. 9,000 years ago, Iztaccíhuatl produced the Buenavista dacitic lava flow. As is obvious, magmatism of the Sierra Nevada Volcanic Range has not kept a continuous north to south migrating path as had been previously surmised. Rather, it has shifted back and forth chaotically throughout its evolution.

Tláloc

Volcanism at the Sierra Nevada Volcanic Range likely started 1.8–1.4 Ma years ago with the construction of Paleo-Tláloc volcano, today buried by younger deposits. The activity continued between 1.07 and 0.89 Ma with the emplacement of dacitic domes, lavas and associated pyroclastic flows (“San Francisco” 1 Ma, “Chicoloapan” 0.9 Ma). Then between 0.94–0.84 Ma, the main edifice of modern Tláloc was built up through the emission of dacitic lava flows. Although Popocatépetl took over as the centre of eruptive activity about 320 kA, Tlaloc reawakened with the emission of rhyolitic magma at 129 kA followed by the emplacement of the El Papayo dacite (118 kA) to the south and Téyotl summit lavas (80 kA).

Tlaloc has always been considered the oldest volcano of the Sierra Nevada Volcanic Range (and extinct), but recent field data have revealed that Tlaloc was very active during late Pleistocene with a series of five explosive eruptions at 44, 38, 33, 31, and 25 kA and the growth of the summit dome. One of these eruptions produced the 1.58 km3 (DRE) Multilayered White Pumice (MWP), a rhyolitic pyroclastic sequence that consist of abundant white pumice (up to 96 vol.%), rare gray pumice, cognate lithics, accidental altered lithics, xenocrysts. The pumice clasts contain phenocrysts of quartz, plagioclase, sanidine, biotite, rare Fe–Ti oxides, monazite, zircon and apatite. Xenocrysts are represented by plagioclase, microcline, orthoclase and quartz likely coming from a deeper plutonic body. Both pumices have a rhyolitic composition (74.98 ± 1 wt.% SiO2 in water free basis) which represents one of the most acidic products of Tlaloc and the entire Sierra Nevada Volcanic Range. (Macías 2011)

Telapón

The inauspicious 260 m high (elevation 3,600 m) steep-sided Cerro Papayo dacitic lava dome marks the vent of the Telapón volcano on the north flank of Iztaccíhuatl formed approximately between 0.38 Ma and 0.34 Ma ago with the emplacement of lava flows and a dome. The 21 cu km compound lava field covers 84 sq km and includes flows that travelled long distances in opposite directions – into the Valley of Mexico and towards the Puebla basin. In addition, the Papayo lavas overlie glacial moraines about 12,000 years old, thus Telapón has been active until the very end of the Pleistocene. The lithology of Telapón shows two periods of activity. First, an andesitic-dacitic Lower Volcanic Event that was emplaced between 1.03 MA and 65 kA, and second, a dacitic-rhyolitic Upper Volcanic Event emplaced between 65 to 35 kA. (Macías 2007).

Photograph of Iztaccihuatl which clearly shows the resemblance to a sleeping woman. (Uncredited photograph, labels added by author)

Iztaccihuatl

The name “Iztaccíhuatl” means “White woman” in the Nahuatl language. Linked to the Popocatepetl volcano to the south by the high saddle known as the Paso de Cortés, it is a 5,230 m (1,560 m prominence) dormant volcanic mountain. Despite its relatively modest prominence, the volume is a staggering 450 km3, which is 100 km3 greater than that of Mount Shasta, Oregon. Iztaccíhuatl began its activity ca. 1.1 Ma ago. From then until 0.45 Ma several volcanic edifices were formed. At that date, the Los Pies Recientes cone was devastated by a Mount St. Helens–type event which destroyed the southeastern flank and produced a massive debris avalanche accompanied by large pyroclastic flows.

The summit ridge consists of a series of overlapping cones constructed along a NNW-SSE line to the south of the Pleistocene Llano Grande caldera. Andesitic and dacitic Pleistocene and Holocene volcanism has taken place from vents at or near the summit. Areas near the El Pecho summit vent are covered in flows and tuff beds younger than glaciation approximately 11 kA, yet GVP states that “The Global Volcanism Program is not aware of any Holocene eruptions from Iztaccihuatl.”

The once glacier-covered peak of Popocatépetl stratovolcano rises above Tlamacas to its north in this photograph from 1968. The sharp peak at right is Ventorrillo, the summit of a predecessor to Popocatépetl, the eroded Nexpayantla volcano. (William Melson)

Popocatépetl

Popocatépetl is the most active volcano in Mexico, having had more than 15 major eruptions since the arrival of the Spanish in 1519 with the most recent in 1947. In Nahuatl, the name means “Smoking Mountain”. Popocatépetl reaches 5,426 m a.s.l. with a prominence of 3,020 m with a base diameter of about 25 km. The crater is elliptical with an orientation northeast-southwest. The walls of the crater vary in height from 600 to 840 m. It lies 70 km southeast of Mexico City and more than one million people live within a radius of 40 km from the summit. According to paleomagnetic studies, the volcano is about 730,000 years old.

Popocatépetl used to be covered by glaciers, but due to increased volcanic activity in the 1990s, the glaciers covering Popocatépetl greatly decreased in size and by 2001 they were gone. Historically, Popocatépetl has erupted predominantly andesitic magma but it has also erupted large volumes of dacite. Magma produced in the current cycle of activity tends to be a mixture of the two.

There are at least four debris avalanche deposits around Popocatépetl volcano. The oldest comes from the failure of the SE flank of Iztaccíhuatl volcano, and the other three come from the flank collapse of paleo-Popocatépetl, the youngest being the 23,000 yr B.P. deposit. The modern volcano was constructed to the south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 AD, have occurred from Popocatépetl since the mid Holocene, accompanied by pyroclastic flows and voluminous lahars that swept through the basins below the volcano.

Some 23,000 years ago a lateral eruption, greater than the 1980 Mount St. Helens eruption, resulted in the lateral collapse of the ancient Popocatépetl cone. The explosion generated a debris avalanche deposit that reached up to 70 km to the South from the summit. The decompression of the magmatic system caused a lateral blast that emplaced a pyroclastic surge deposit accompanied by a Plinian eruption column which deposited a thick pumice-fall layer on the southern flanks of the volcano. The column then collapsed and formed an ash flow that charred everything in its path. The deposit reached up to 70 km from the summit, covers an area of 900 km2, and if we assign an average thickness of 15 m, a volume of 9 km3 is obtained. This deposit overlies paleosoil that contains charred logs radiocarbon dated at 23,445 ± 210 yr. Disseminated charcoal found in the ash flow deposit yielded an age of 22,875 +915/−820 yr. (Macías)

During the past 20,000 yr the explosive activity of Popocatépetl has been characterized by four major events (14,000, 5000, 2150, and 1100 BP) and four minor events (11,000, 9000, 7000 and 1800 BP) The events that occurred at 5000 and 1100 BP had a similar evolution. They began with hydromagmatic explosions that dispersed wet pyroclastic surges up to 20 km from the summit. These explosions opened the magmatic conduit, decompressed the magmatic system, and formed >25-km-high Plinian column.

From our perspective, it is of interest to note that the last three Plinian eruptions of Popocatépetl coincide with three important events in Mesoamerican history: The 3195–2830 B.C. eruption coincides with the 3114 BC beginning of the Mesoamerican Calendar. The 215 BC eruption coincides with the transition from the Preclassic to the Classic period. The last major eruption, which probably occurred in 823 AD, coincides with the Classic-Postclassic periods transition.

The Parque Nacional El Tepozteco is at the centre of the Chichinautzin volcanic field. It consists of a small temple to the Aztec god Tepoztecatl, a god of the alcoholic pulque beverage. (unearthingarchaeoblog)

The Chichinautzin Volcanic Field

The Chichinautzin volcanic field contains more than 220 Pleistocene to Holocene monogenetic vents and covers a 90-km-long, E-W-trending area immediately south of Mexico City. It is formed primarily of overlapping small cinder cones and shield volcanoes with a mainly basaltic-andesitic to andesitic composition with a thrachytic component as well as some dacite evident. The highest peak of the Sierra Chichinautzin is the Volcán Ajusco lava-dome complex at 3930 m a.s.l. There have been at least eight eruptions within the past 10,000 years with the most recent about 1670 radiocarbon years ago (~340 AD) from the Xitle scoria cone. These eruptions have typically been VEI 3 with one registered as a VEI 4. A very modest estimate based on an oval 60 x 90 km with an average emplaced height of 250 m yields a figure of 1,050 cubic km for the volume of the dome but the true figure could be more than double that. From the list of sources in the GVP entry for the Chichinautzin volcanic field, it would seem that some individual cones, vents and flows have been studied, but not the feature as a whole. What is it? What is its true age? Why is it so large, far larger than the initial shield deposited during the first development stage before volcanism shifts to construct (a series of) stratovolcanic edifices? Is there a significance to its position on the same isoline above the subduction zone as Pico de Orizaba, Popocatépetl and Nevado de Toluca?

Summing up

The geological setting of the Mexico City basin is unusual in that the subduction zone makes an almost 90-degree angle and that the major volcanoes do not follow the subduction zone but rather form lines at right angles to it. Instead of showing a neat progression, volcanic activity has been shown to jump “chaotically” (Macías 2011) both geographically as well as petrologically. There is a marked absence of identified caldera structures in the area, yet in the middle of it, right at the southern edge of the city limits, lies a more than 1,000 km3 large Pleistocene to Holocene dome structure that has been active until recently, one that is not well studied.

In addition to this, the Nevado de Toluca volcano has already produced eruptions sufficiently large to deposit ignimbrites at distances greater than 25 km from its summit and Popocatépetl clearly has the potential to do so. Both these volcanoes (and Iztaccihuatl) have suffered several major edifice collapses where deposits have been traced to distances greater than 55 and 70 km respectively.

With almost 30 million people living within 100 km, Mexico City will remain on our list until the mysteries of why the “currently and recently active” volcanoes of the TMVB align perpendicular to the subduction zone as well as where and why the very large, caldera-forming eruptions (VEI 6 to 7) have disappeared to have been unravelled. It will remain on our list until we have a thorough investigation of the past and likely future evolution of the gigantic Chichinautzin volcanic field as well as a better understanding of the risks posed by the large stratovolcanoes in the vicinity.

The more I delved into this subject, the more intricate it became and the more I realised just how little I understood. The TMVB as it passes the Toluca – Mexico City – Puebla area once fully investigated may well deserve a place higher up on the list (or possibly even be struck from it), but with the material and understanding at present, we will leave it at a provisional fifth place on our list.

Volcanoes in Space

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We live on a spectacular, dynamic planet. Geological processes like volcanism and quakes were long thought to be unique to Earth, then again we once thought the planet was flat! As we further our exploration of our solar system and beyond we have witnessed that many other planets display activity from moon quakes to eruptions on distant moons of Jupiter.

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In June Venus broke in to mainstream media as the ESA announced they had evidence of current volcanic activity on the second planet from the Sun. Venus’s dense atmosphere has long been blamed on a violent eruptive past, but it was thought that this had long since calmed. Then last month NASA released images of Pluto which suggested recent resurfacing, so where is there volcanic activity within our solar system and how does it compare to activity here on Earth? Here is a basic over view of volcanology with our Solar System other than here on Earth.

Mercury

Starting with the planet nearest the  Sun with a small, quiet Mercury. When people first glimpsed at the planets scarred surface instantly it was thought that the impact from meteors or asteroids in the past were the most likely cause. Even when the suggestion was made that volcanism could be a cause for at least some of the topography it was said that the planet did not have the volatiles available for such explosions. These ideas were strongly refuted in 2008 when NASA’s MESSENGER mission began to feed back clearer images of the surface then we had before. They showed clear signs of pyroclastic deposit at 51 sites, all of which showed different degrees of erosion indicating they had happened at varying stages in the planets history. There was also evidence of compressional features such thrust faults leading us to belive that Mercury is more geologically active (or at least has been) then we previously thought.

Venus

Venus’s surface is scared with more volcanic features than any other planet in our solar system. Its dense, toxic atmosphere is believed to be due to the release of volatiles during its explosive past.Huge shields such as Maat Mons and Sapas Mons have appeared reminiscent of those of Earth such as Muana Loa with composition of lavas most likely to be a fluid basaltic or occasional carbonatite. Although some similarities are there Venus shows no sign of tectonic activity such as the liner volcanic chains or subduction arcs we have here on Earth. Volcanism appears to be limited to upwelling similar to hotspots on Earth evident in the large Hawaiian style shields.

Despite all this evidence of volcanism it appeared to have long since ceased until ESA’s Venus Express completed its 8 year mission getting up close and personal with the planet last year.

Radar imagery detected several hot spots along the surface indicating at the very least younger lava flows then we previously thought. It is still open for debate for the age of such flows or if even an eruption or two are taking place up there while I type. The one thing that Venus Express has proved is that activity has occurred in more recent geological time than we had previously thought.

The Moon

Getting closer to home we have our natural satellite, the Moon. It’s surface separated in to two distinct regions; Lunar highland and maria.  The age of the two regions were hinted at by the amount of impact scaring. The older the rock the more impact craters tend to cover its surface; the highlands. The dark patches, visible to even the naked eye, are the maria, volcanic resurfacing of these areas been they are less scared by impacts. Basaltic lava flows dated predominately at 3.8-3.2 Ga, believed to be caused by upwelling in ancient impact basins due to thinness of the crust. Unlike terrestrial basalt, samples from the Mood indicate a much lower SiO2 content (<45%).

Patches reveal recent lunar volcanism

But much like Venus, where we thought things had calmed billions of years ago, in 2014 NASA’s Lunar Reconnaissance Orbiter (LRO) allowed us to see our perception of Lunar volcanism was also potentially wrong. It was perceived volcanism came to a rather abrupt stop roughly 3.2 Ga ago but LRO was able to pick out rock formations and deposits which would not have been visible from Earth. These new features were termed Irregular Mare Patches (IMP). These new images suggest volcanism did not stop abruptly as previously thought, but petered off over millenia ending as little as 100 million years ago.Figure 4 shows one such IMP deposit called Maskelyne indicative of smaller, younger eruptions than what we believed formed the maria in the first place.

This leads to a whole new train of thought when it comes to lunar dynamics. Recent volcanism means the Moon’s interior was hotter for longer then we believed, and if so is it still capable of eruptions?

Io

Io is one of my favourite aspects of extraterrestrial volcanism, and to be fair volcanology in general. Despite only being one of Jupiter’s moons, it claims the title of our Solar Systems most volcanically active body. Io’s most famed images captured a sulphurous eruption column which breached Io’s atmosphere climbing 140 kilometres from the surface from the  Pillan Patera caldera. And also in the centre of the image the Prometheus Plume, a 76 kilometre eruption column which cast and amazing shadow of the surface. The first time the Prometheus Plume was spotted was during the Voyager flybys in 1979. It was then captured several times in exactly the same place at a similar altitude by Galileo during its orbital of Jupiter from 1995 to 2003. This suggests an eruption of continuous intensity for over 18 years!!!

Io: The Prometheus Plume

Volcanism is believed to be driven by strong tidal forces. Io is not only subject to Jupiter’s gravitational pull but also that of two of its other satellites; Europa and Ganymede, both much larger than Io. The surface is full of huge caldera’s and lava flows, much longer that we see on Earth. Magmatic composition is believed to vary from ultramafic basaltic flows to much more sulphur rich melts which lead to flows in excess of 2400  °C. It is thought that as many as 400 active volcanoes cover the surface making it a very explosive environment indeed!

Enceladus

Cryovolcanism is a concept that had been batted around for a while on form or another. A volcano erupts a melt based on the composition of the underlying crust and in some cases mantle. On Earth we have a wide variation of silica based magmas and even the rare instances of carbonatites, but what of an icey body rich in water, ammonia or methane?

When the Voyager missions passed Enceladus in the early 1980’s it was suggested that the satellite may be geologically active due to its smooth surfaces and location close to the E Ring. It wasn’t untill NASA’s Cassini mission in 2005 that proof of cryovolcanism on the body really came to light.

The first detection of the icy plume came on February 17th. Then a second event was witnessed July 14th and this time Cassini flew through the gas cloud enabling on board instruments to tell us the composition; predominately water vapour with traces of nitrogen, methane and carbon dioxide. Visual confirmation came in the November with plumes of icey particles streaming from the bodies south polar region. A subsurface ocean under the south polar region is believed to be the cause of a thermal anomaly in the area which could be fuelling volcanic activity, although tidal heating my also have a hand.

Triton

In 1989 Voyager 2 passed by Neptune’s moon Triton and took images to give us an insight to these far out bodies and managed to find further proof of cryovolcanism in our Solar System. Several geyser like eruptions were spotted with plumes as high as 8 km above the surface. The entire surface looked relatively young with such fewer impact craters than other bodies the mission had encountered, another indication it was very geologically active.

Pluto and Charon

NASA’s New Horizons mission sent back amazing images in July of not only Pluto, but also its satellite Charon. Both exhibited relatively young surfaces, Charon more so than Pluto has huge patches barely dented by impacts suggesting recent resurfacing. Pluto is home to mountainous regions which have be likened to the Earth’s Rocky’s and huge nitrogen filled glaciers. Although no clear evidence of volcanism was seen as of yet, it is obvious that Pluto is more geologically active then we previously thought. It will take another 16 months for all the data collected to return to Earth so in time we may have evidence of at least one or two more volcanic bodies within our system!

There is still much we don’t know about the dynamics of volcanoes, both here on Earth and on other planetary bodies. One thing we can conclude is the further we explore the universe the more we will learn geologically which we can apply to our own planet and equally, exploring our own planets workings can help us understand others.

Figure 1. Painting; http://www.astroart.org/#!volcanoes/c440

Figure 2. Mercury; http://space.stackexchange.com/questions/2302/how-tectonically-active-is-mercury

Figure 3. Venus poster; http://www.esa.int/spaceinimages/Images/2015/06/Evidence_for_active_volcanoes_on_Venus

Figure 4. Moon; http://www.latimes.com/science/sciencenow/la-sci-sn-moon-volcano-recent-nasa-lunar-20141014-story.html

Figure 5. Io; http://www.nasa.gov/multimedia/imagegallery/image_feature_758.html

Figure 6. Enceladus diagram; https://en.wikipedia.org/wiki/Enceladus#Cryovolcanism

Figure 7. Enceladus; https://www.pinterest.com/astrobella/volcanoes-fire-and-ice/

Figure 8. Pluto; http://www.bbc.co.uk/news/science-environment-33543383

The New Decade Volcano Program; #6, Bali

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A week later than posted on Volcano Cafe, here is number 6 on the guys proposed list! Introducing the dangers of Bali…

Romantic Paradise Destination – The New Decade Volcano Program #6, Bali

Sunset from the 3,148 m high summit of Gunung Agung. The peak in the distance is G. Abang, a remnant of a far loftier peak, Ancestral Batur. (WikimediaCommons, photo by Mrllmrll).

It has often been pointed out that the deadliest volcano is the one you did not know about. This is our dilemma. When you try to identify the potentially most dangerous ones, by necessity you have to go out on a limb to find those that are not well known nor well studied and there is always the chance to end up with egg on your face. But in this we are not alone. As an example, it was long thought that a particularly heavy layer of volcanic dust in ice core samples dated to c. 3650 BP belonged to Thera. Only recently has most of this been identified as belonging to the far larger, contemporaneous, 100km3 DRE Aniakchak eruption in the Aleutians, Alaska.

When it comes to large volcanic eruptions, one of the more striking features is the Sunda Arc that runs from Sumatra via Java and the Sunda Strait through the Lesser Sunda Islands. Sumatra is home to the Toba caldera, source and result of the largest volcanic eruption in the past 100 kA. Recently, a vast body of magma underlying Java was discovered, one that feeds that islands prodigious volcanic activity. But of the southern part of this arc; the Sunda Strait and the Lesser Sunda Islands, little is known. Yet this part of the Sunda Arc is home to two of the largest volcanic eruptions of the past 1,000 years; Rinjani (~1257 AD, <80 km3 DRE) and Tambora (1815, 33 – 41 km3 DRE). Sufficient to say, was there a repeat of either of those eruptions today, the islands hosting these giants are home to some 4½ million people each and neither such VEI 7 blast would be survivable. As both had “mega colossal” eruptions recently geologically speaking, neither is a good candidate for another one in the foreseeable future. But on the premise that a similar magmatic feed into a similar geological setting will most likely result in similar volcanic activity, let’s take a closer look! Lightning did after all strike twice here within the past millennium!

The Sunda Arc from Eastern Java through the Sunda Strait and the Lesser Sund Islands where the Australian plate subducts under the Sunda Plate at a rate given as 6-7 cm per year, relatively high. Note that for Sumatra and Western Java, the subducting plate is the Indian plate. The names of the Islands is green, active volcanic complexes, calderas and the larger stratovolcanoes are denoted in red. Sangenes (yellow) is thought to be extinct.

From a birds-eye view, this area is characterised by the formation of very large stratovolcanic cones with a prominence in excess of 3 km (eg Raung, ancestral Catur, Ancestral Batur. Agung, Rinjani, Tambora and the partly submarine Sangeang Api), volcanic complexes (eg. Biau, Buyan-Bratan and Batur) and 10-15 km calderas (eg. Biau, Bedegul, Batur). It all comes together on Bali, tropical island paradise and the place to go for a romantic holiday. Apart from the 1963 VEI 5 (5.3) eruption of Gunung Agung, little is known about the volcanism of Bali.

Bali

With a population of 4,225,000 as of January 2014, Bali is home to most of Indonesia’s Hindu minority which according to the 2010 Census constituted 84.5% of the island’s population. Just over a quarter of a century ago, the economy was mainly based on agriculture. Before the 2003 terrorist bombings, over 80% of the economy was tourism-related and Bali had become the richest of all Indonesian territories. Annual tourism is in excess of eight million with five being Indonesian and the remaining three international. To crown it all, Bali was host to the 2013 Miss World pageant.

The main tourist locations are concentrated to the South; Sanur on the east coast which once was the only tourist location, Kuta with its beach and close to the Ngurah Rai International Airport, Ubud in the centre of the island and the newer development Nusa Dua and Pecatu. Kuta, the main tourist location, lies 55 km from the centre of the Buyan-Bratan volcanic complex, 61 km from the centre of the Batur Caldera and 60 km from the peak of the 3,031 m high Gunung Agung, The town of Ubud is basically at half that distance while Dempasar, the capital with over 800,000 inhabitants, is within 50 km of all three.

The crust beneath Bali Island is about 18 km thick and has seismic velocities similar to those of oceanic crust (Curray et al, 1977). The depth of the Benioff Zone beneath the Batur Volcano is 165 km, which has been computed by multiple linear regression analyses (Hutchison, 1976). The depth of the seismic zone beneath the arc reaches to approximately 650 km depth between Java and Flores. The oldest widely exposed rocks are lower Tertiary shallow marine sediments, which are intruded and overlain by plutonic and related volcanic rocks in a zone only slightly south of the present-day volcanic arc (Bemmelen, 1949). The rocks of the Sumatra to Bali sector range from tholeiitic through calc-alkaline to high-K calc-alkaline series.

Geologic map of Bali Island. Note the extent of the “Buyan-Bratan and Batur Tuffs and Lahar deposits” and compare with the previous map of Bali showing the main settlements. (After Purbo-Hadiwidjojo, 1971)

Volcanism in Bali is concentrated to three areas, the Buyan-Bratan volcanic complex which formed roughly 100,000 years ago but holds several young stratovolcanic cones to the SSW, the Batur Caldera which formed <100,000 to 25,000 years ago and has the highly active stratovolcanic cone of Batur. Both areas contain large lakes within the caldera perimeters. Finally, there is Gunung Agung which had a powerful VEI 5 eruption as recently as 1963. However, the eruptive record of Agung extends no further back than to the 1808 VEI 2 eruption and that of Batur to a VEI 2 eruption in 1804. Being located just south of the Equator, the tropical climate and vegetation quickly covers whatever volcanics that have been deposited. This may create a false sense of security.

Buyan-Bratan Volcanic Complex

The Buyan-Bratan volcanic complex is also known as the Bedegul caldera, Bratan caldera, Catur or Tjatur caldera. The southern caldera wall has disappeared beneath a superimposed field of young, heavily vegetated stratovolcanoes including Gunung Batukaru (2,276 m), Adeng (1,826 m), Pohen (2,063 m), Sengayang (2,087 m), Lesung (1,865 m), Tapak (1909 m). Although the ancestral volcano is known as Mt Catur, the location of today’s Catur (2,096m) on the NE calera rim argues that it may not be a volcano even if it is sometimes referred to as being one.

The age of the 6 x 11 km Bedegul caldera which formed when ancestral Mount Catur collapsed is unknown although it must be substantially older than ~30,000 years and possibly even hundreds of thousands of years. The field of young stratovolcanoes to the SW, the Byan-Bratan Volcanic Complex, is heavily vegetated, thus the latest period of activity remains unknown but has been tentatively placed hundreds or thousands of years ago (Wheller, 1986). Two of those stratovolcanoes, Tapak and Lesung must have formed after the last large eruption of the nearby Batur Caldera as they not covered by deposits of its youngest dacitic pumice eruptions. As this has been dated to 20,150 years ago, these stratovolcanoes with prominences of 625 and 669 m respectively as measured from the surface of Lake Beretan must therefore be less than this age. Inside the caldera, geothermal activity is exploited at the Buyan-Bratan geothermal power plant and there are at least a dozen hot springs in the area.

The municipality of Beretan is a major Hindu enclave and contains a Shiivaite temple, the Bratan Bali. (Indonesia Tourism)

The outline of the remaining caldera walls suggest that there may have been two events; the first forming the 9 to 10 km diameter Western part with the stratovolcanic cone of Tapak forming subsequently near the centre, the second forming the smaller 5.5 to 6 km diameter Eastern part. Very tentatively and assuming that the calderas were formed by the subsequent collapse of those edifices following a major eruption, also assuming that the ancestral volcanoes were similarly steep to the nearby Mount Agung, we can make an educated guess at the size of those eruptions. Ancestral Catur (Catur A) would have been about 3,300 m high (a.s.l.) and the caldera bottom, allowing for subsequent infill, would have been about 600 to 800 m deep as measured from the remaining walls. This yields a figure on the order of 52 + 16 = 78 km3 or borderline VEI 7 for the larger caldera, Catur A. Catur B would have been about 2,400 m a.s.l. and the caldera ~500-600m deep as measured from the remaining walls prior to infill. This results in figures of 11.3 + 4.7 = 16 km3 or a small to medium-sized VEI 6 eruption. Please note that this is speculation on my part! No doubt better-informed readers will hasten to correct my assumptions from a position of superior knowledge!

The southernmost stratovolcano of the Buyan-Bratan volcanic complex is the 2,276 m high Batukaru, which means "coconut shell" in Balinese. It has a prominence of ~1,500 m as its edifice can be traced to just below the 800 m topographic isoline. (Bali Foto Galerija)

Apart from the already mentioned Gunung Tapak (1909 m), the volcanic field subsequent to the caldera forming event(-s) includes at least another five major stratovolcanoes – Batukaru (2,276 m), Adeng (1,826 m), Pohen (2,063 m), Sengayang (2,087 m), Lesung (1,865 m). There is no information on any eruptive activity but as previously stated, due to the tropical climate and vegetations, all we can definitely state is that there has been no activity in the past two to three hundred years as there is no historical record of any. With at least two of them being younger than ~20,000 years, the likelihood is that all have been active recently, geologically speaking. What their presence does suggest however, is that the original magmatic system of ancestral Catur (Catur A & B) has been well and truly destroyed and that if in the future, there is renewed volcanic activity in the Buyan-Bratan volcanic complex, this will be from one or more of these young stratovolcanoes and most likely not greater than VEI 3, possibly a very small VEI 4 eruption in the sense that the eruption of Eyjafjallajökull in 2010 counts as one. As an example, at Tapak there are at least five layers of scoria separated by four layers of paleosoil, indicative of at least five periods of extended eruptive activity separated by four periods of repose. (Watanabe et al:2010). Watanabe and his co-authors repeatedly lament the fact that while Batur Caldera nowadays is relatively well studied, almost no research whatsoever (apart from their own exploratory field study, author’s note) seems to have been undertaken of the less easily accessible Buyan-Bratan Caldera and volcanic complex.

Batur Caldera

Ancestral Batur was an approximately 4,000-meter high stratovolcano, nearly a kilometre higher than present-day Agung (3,148 m), which had an enormous eruption in prehistoric times to form the outer, 10×13.8 km caldera around 29,300 BP which today contains a caldera lake, Danau Batur. The inner 7½ km caldera was formed at about 20,150 BP.

Gunung Batur (1,717 m.a.s.l., prominence 700 m) is a small stratovolcano in north-central Bali and its most active. It has several craters and remains active to this day. The first historically documented eruption of Batur was in 1804 and it has erupted over 20 times in the last two centuries (VEI 1 – 2). Larger eruptions occurred in 1917, 1926 and 1963. Clinopyroxene from the 1963 eruption of Batur record crystallisation depths between 12 and 18 km, whereas clinopyroxene from the 1974 eruption show a main crystallisation level between 15 and 19 km. Furthermore, plagioclase melt thermobarometry indicates the existence of shallow level magma reservoirs with depths between 2 and 4 km for the 1963 eruption and between 3 and 5 km for the 1974 event (Geiger:2014). This suggests the existence of a very large and rather deeply lying primary or lower magma chamber as well as a moderately substantial upper magma chamber.

The term “Batur” often refers to the entire caldera, including Gunung Abang, Bali’s third-highest peak, which is situated along the rim. Batur is a popular trekking mountain among tourists, as its peak is free from forest cover, offers spectacular views and is easily accessible.

The substantial lava field from the 1968 eruption (Batur III, VEI 2) that began on Jan 23rd and ended on Feb 15th 1968. (Martin Moxter)

Batur has produced vents over much of the inner caldera, but a NE-SW fissure system has localized the Batur I, II, and III craters along the summit ridge. Historical eruptions have been characterized by mild-to-moderate explosive activity (Strombolian?) sometimes accompanied by effusive emissions of basaltic lava flows from both summit and flank vents which have reached the caldera floor and the shores of Lake Batur in historical time.

The Batur caldera formed in two stages. Through radiocarbon dating, we have a relatively good idea of when. The first and larger of these is associated with the 84 km3 dacitic ignimbrite known as the “Ubud Ignimbrite” which in locations is over 120 m thick. About 29,300 years BP, Ancestral Batur had a “mega-colossal” VEI 7 eruption which caused a steep-walled depression about 1 km deep and over ten km in diameter. The second ignimbrite, the 19 km3 dacitic “Gunungkawi“ Ignimbrite”, erupted about 20,150 years BP from a large crater in the area of the present-day lake. The second eruption triggered a second collapse, which created the central 7½ km diameter circular caldera, and formed a basin structure. Both the Ubud and Gunungkawi Ignimbrites are of a similar dacitic composition although the latter is more mafic, white to red in main with less than 10% dark grey to black dacitic pumice clasts. In the case of the second of these ignimbrite, two different cooling layers were identified. The lower, thus first ejected, is finely grained and welded, hence it was far hotter. In places, it is between 5 and 20 m thick. The upper, coarser, partially welded and hence “cooler” unit has suffered much erosion but is in places up to between 50 and 70 metres thick. The calculated volume of erupted material for the Ubud (84 km3) and Gunungkawi (19 km3) Ignimbrites coincide with and are proportional to the size of related collapses of Caldera I (80 km3) and Caldera II (18 km3).

After these eruptions, there were two further ignimbrite-producing eruptions, both mainly intra-caldera. The Batur Ignimbrite is a densely welded dacitic ignimbrite, typically 50 – 200 m thick, which at one point overflows the caldera rim to form 30 to 70 m thick layers of non-welded ignimbrite. The Blingkang Ignimbrite is a non-welded to moderately welded intra-caldera ignimbrite deposit between 5 to 15 metres thick. Sparse charcoal clasts scattered in this sheet give an age of 5,500 ± 200 years B.P. The thick phreatomagmatic and surge deposits which are found below the ignimbrite indicate that this was preceded by phreatomagmatic eruptions. In addition to these four sequences, basaltic to basaltic andesite lavas and pyroclastic deposits are inter-layered with and underlie the ignimbrite sequences, particularly in the southern slope of the caldera.

In spite of the frequently erupting modern Gunung Batur with its moderately sized eruptions, this caldera cannot yet be said to have shot its bolt due to the implied existence of a very large magma reservoir, one that was apparently not destroyed by the caldera-forming eruptions. Both the Batur and Buyan-Bratan calderas illustrate a recurring theme where first a very large stratovolcanic edifice is built after which there is a substantial VEI 7 ignimbrite-forming eruption followed by the formation of a dacitic to andecitic dome complex after which a large, ignimbrite-forming VEI 6 eruption follows. Even if one of these volcanic complexes almost certainly is no longer capable of such large eruptions and the other probably not in the foreseeable future, there remains one gigantic stratovolcano on Bali, one that has dimensions of 8 x 11 km as measured at the 1200-m isoline, 2,000 m above which its somewhat truncated summit towers.

Gunung Agung

Gunung Agung photographed from about 60 km to the south during an overflight of the main tourist areas of Bali. Except for the extreme bottom of the picture, the entire plain visible is covered in ignimbrite deposits from the Batur I eruption of about 29,000 BP (WikiMedia Commons)

Located in the eastern part of Bali, Mt Agung is a young basaltic to andesitic composite volcano. Bordered to the east by the inactive or extinct volcanic cone Seraja, to the south by an ancient volcanic complex and to the NW by a valley that separates it from the Batur volcanic complex, Agung goes all the way down to the Indian Ocean to the NE and through a long unimpeded decline over the Buyan-Bratan and Batur ignimbrites and lahar deposits to the SW and WSW, all the way to the capital Denpasar and beyond. South of Agung, there are older Tertiary volcanic deposits as well as remnants of coral reefs. The present-day volcano is surrounded by older Quarternary andesitic and basaltic-andesitic lavas and pyroclastic deposits, something that has prompted the conclusion that Agung overlies an older caldera formation (S. Self et al:1979).

The eruptive record of Agung goes back only to 1808 when the volcano had a VEI 2 eruption. Since that date, Agung erupted again in 1821 (uncertain) and 1843, both VEI 2 eruptions after which it remained dormant for 120 years until the great eruption of 1963. Prior to 1808 is a big unknown, although the relative symmetry of the mountain, the state of its upper slopes as well as a comparison with similar volcanoes suggests that Agung would have erupted relatively frequently.

On February 18th 1963, locals reported hearing a loud explosion after which a dark eruption cloud rose over Agung. The first explosions were probably phreatic or phreatomagmatic. On February 24th, highly viscous lava oozed over the northern slope, 0.5-0.8 km wide and 30-40 m in height. It was moving so slowly that it took 18 to 20 days to reach 500 m a.s.l after travelling some 7 km down from the peak. This works out at a speed of about 4 mm per second or 14 m per hour. The volume of lava erupted was estimated to be on the order of 0.05 km3. After this, the eruption continued with a combination of effusive and explosive events.

On March 17th came the main eruption. The eruption cloud reached 8-10 km above the volcano but the lower portions fell down the slopes as nuees ardentes that travelled with a speed of about 60 km/hour up to 12-15 km from the crater down the valleys to the south and east. From this description, it seems the eruption was peléean. The pyroclastic flows destroyed many villages around the volcano and caused the deaths of many people living near the river valleys. Estimates are that 820 people were killed by the pyroclastic flows, 163 people were killed by ashfall and volcanic bombs and a further 165 people were killed by lahars.

A comparison between the lavas erupted by Batur and Agung reveals that while Batur tends to erupt more trachytic magmas, the magmatic system of Agung produces more evolved magmas. The comparison between the historic and modern lavas indicates that, at present and probably, the Batur caldera does not produce the types of more evolved magma required to cause ignimbrite-forming eruptions. Unfortunately, it seems the lavas of Agung have not been similarly analysed and the data is based on a single eruption, that of 1963. (H. Geiger:2014)

For the 1963 Agung eruption, results from clinopyroxene melt thermobarometry suggest dominant crystallisation levels between 18 and 22 km depth. Plagioclase melt thermobarometry indicates the existence of shallow level magma reservoirs, with depths between 3 and 7 km for the 1963 eruption, located around the boundary between the (upper) sedimentary and the oceanic type mid- to lower crust. The deep magma storage regions notably coincide with lithological boundaries in the crust and mantle beneath Bali, at the boundary between MOHO and crust, while the shallow reservoirs are consistent with recent geophysical studies that point to regional shallow level magma storage. An along-arc comparison reveals this trend to be characteristic of Sunda arc magma storage systems. According to Harri Geiger, the author, the result “highlights the utility of a thermobarometric approach to detect multi-level systems beneath recently active volcanic systems.” (Geiger: 2014)

Summary

As was remarked at the beginning; a similar magmatic feed into a similar geological setting will most likely result in similar volcanic activity. This premise is further substantiated by the conclusion presented by Geiger, that the deep magma storage regions notably coincide with lithological boundaries in the crust and mantle and that this is a characteristic of the Sunda Arc. The conclusions that can be inferred from these observations are:

  • Very large caldera-forming, ignimbrite depositing eruptions VEI 6 to 7 are a characteristic of Lower Sunda Arc volcanism
  • The location of the deep magma reservoirs is such that these are not likely to be destroyed by the caldera-forming eruptions unlike those at other locations (e.g. Roccamonfina, Mt Mazama, Aniakchak)
  • Bali contains no less than three such volcanic systems of which the currently inactive Buyan-Bratan Volcanic complex is in a phase of stratovolcanic dome construction, the Batur Caldera is in the process of rebuilding a main stratovolcanic edifice while the Agung system is meandering towards the end of that phase
  • All three volcanic systems pose potential hazards to the Balinese population and require further studies as well as systematic monitoring
  • Of the three, the greatest danger is posed by the Agung system and at present, there is insufficient data to rule out a very large, caldera-forming and or ignimbrite depositing eruption

For these reasons, Bali is our proposed number six on the New Decade Volcano program.

Henrik

Acknowledgement: I am indebted to Shérine France for finding and bringing Watanabe et al 2010 and Geiger 2014 to my attention.

Igan S. Sutawidjaja, “Ignimbrite Analyses of Batur Caldera, Bali, based on C14 Dating”, Jurnal Geologi Indonesia, Vol. 4 No. 3 September 2009: 189-202. http://oaji.net/articles/2014/1150-1408334776.pdf

K. Watanabe, T. Yamanaka, A. Harijoko, C. Saitra and I W. Warmada; ”Caldera Activities in North Bali, Indonesia”, Journal of S.E. Asian Applied Geology, 2010
http://geologic-risk.ft.ugm.ac.id/fresh/jsaag/vol-2/no-3/jsaag-v2n3p283.pdf

O. Reubi & I. A. Nicholls, “Structure and Dynamics of a Silicic Magmatic System Associated with Caldera-Forming Eruptions at Batur Volcanic Field, Bali, Indonesia”, Victorian Institute of Earth and Planetary Sciences, 2005. http://petrology.oxfordjournals.org/content/46/7/1367.full.pdf

H. Geiger, “Characterising the Magma Supply System of Agung and Batur Volcanoes on Bali, Indonesia”, Uppsala 2014
http://uu.diva-portal.org/smash/get/diva2:759515/FULLTEXT01.pdf

The Decade Volcanoes

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As I reblogged my last post, a revision of the Decade volcano list by the authors of VolcanoCafe, I thought before I bring you the new list I should really explain what the original one actually was!

As mentioned in one of my earliest articles, the list was complied in 1990 by the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) a nongovernmental society. The aim was to select the worlds most hazardous volcanoes and put measures in place to keep a closer eye on them and raise awareness across the globe on the threats they pose, for a decade (1991-2000 The UN’s International Decade of Natural Disaster Reduction). Based on varied criteria from historic eruptions to local populations, the following made the cut;

Figure 1. USGS map of the decade volcanoes.

15 Years on the list is still going all though monitoring in some areas may have slackened slightly. It has seen some success such as the diversion of a lava flow on Etna back in 1992 and has helped form a better understanding of phreatic eruptions on Taal. It has sadly also come at great loss on several occasions as well. Despite increased monitoring of Unzen in 1991 pyroclastic flows killed 43 including volcanologists Katia and Maurice Krafft and Harry Glicken.  And even closer to the project, in 1993 the Decade Volcano conference took place in Pasto, Columbia an expedition from the conference to the Galeras crater occurred on February 14th when the volcano suddenly erupted. 3 tourists and 6 volcanologists including Professor Geoff Brown, Head of Department of Earth Science at the Open University, all lost their lives.

Many volcanologist are sceptics and/or critics of the program, hence the call for a revamp. Personally I feel any thing which promotes volcanic awareness is great all though there are some which need much more than others. Volcanoes are ever evolving and unlike most geological features can change in minutes rather than millennia and therefore prehaps a decade is too long for reviews of such a program. I know which have made my list, it will be interesting to see what makes the cut for the guys at VolcanoCafe!

Figure 1. http://listas.20minutos.es/lista/volcanes-de-la-decada-decade-volcanoes-301649/

Eruptions Update

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Turrialba

Costa Rica’s Turrialba has been rumbling for about a week now and at 9pm UTC Monday 4th it gave a moderate eruption which has coated as far as the country’s capital, San Jose, in ash 60km away. An ash column stood at just 2.5 km in from the eruption which lasted little over half an hour. The Juan Santamaría International Airport was closed for under 12 hours as staff worked through to clear the run way of ash, the aviation code has since been lowered and flights have resumed normal operation. When Turrialba started erupting back in March it left the airport closed for days, luckily this seems to be a much smaller eruption.

Turrialba, Costa Rica

Bulusan

Bulusan in the Philipeans let off a small phreatic eruption at 1.30 local time on Friday 1st May. The eruption which only lasted 5 minutes was followed by 40 volcanic tremors. Philvolcs have left the alert at 0 with it belived further activity is unlikely but the 4 km permanent danger zone is being kept in place. Local residents have also been advised to be watchfull of lahars and sediment heavey stream flows due to the heavy rain in region.

Hakone

JMA are sending a team to look in to increased seismicity in the Hakone hot springs region. The earthquakes are believed to volcanic tremors which have been increasing at a shallow depth since late April. Inflation of the volcanic edifice is also being looked into. Alert remains low.

 

 

Eruption Update

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I may have bee quiet on eruption updates lately but that is far from meaning our restless Earth has been quiet. Here is some of the recent updates.

Kilauea 

As Kilauea has been in a constant state of eruption since 1983, some don’t consider changes in activity as news. However as the June 27th lava showed us this relatively calm giant still poses a threat to people.

USGS reports suggest that the summit is still inflating; 7.5 microradians were recorded in the past week alone. Over the weekend we saw rapid filling of the Halema’uma’u crater from a depth of 90 ft from the crater rim to within 10 ft by Sunday lunch time. Yesterday (April 29th) the webcam observed small explosions and spattering with rock falls as the crater began to overflow.

Seismicity remains at an increased level towards the summit and East rift zone where wide spread breakouts from the eruption site are active as close as 8 km of Pu’u ‘O’o. There has be net inflation of Pu’u ‘O’o over the past week but not as significant as at the summit. As the June 27th Lava flows nears its 1 year anniversary incandesance indicates that surface flows remain active northeast of Pu’u ‘O’o.

Calbuco

Although the more explosive phase of the eruption seems to have died down, there are still high ash emissions and flight disruption is still an issue across both Chile and Argintina with ash plumes trailing to the north and south east at just over 1.5 km high. The 20 km exclusion zone is still inplace however it is belived that some people have returned to their homes within the area with maximum displaced 6,514 at the begining of this week. Seismicity has since declinded but it is still under observation.

Sinabung

Collapse of the lava dome on April 28th caused a pyroclastic flow to surge down the flanks. Luckily exclusion zones are still in place from activity over the past few months. The Darwin VAAC  said an ash columb exceeds 14,000 ft although satalitte confirmation has not been possible due to cloud coverage.

Aira

JMA reported that 29 explosions from Showa Crater at Aira Caldera’s Sakurajima volcano ejected tephra as far as 1,300 m during 20-24 April. Nine of the explosions generated ash plumes that rose 3 km above the crater rim; one explosion, on 24 April, produced an ash plume that rose 4 km. Incandescence from the crater was visible on one night. The Alert Level remained at 3 (on a scale of 1-5). Based on JMA notices, the Tokyo VAAC reported that explosions during 22-28 April generated plumes which rose to altitudes of 1.5-4.9 km and drifted S, SE, E, NE, and N.

Tungurahua

Moderate-to-high seismic activity at Tungurahua during 22-28 April, characterized by long-period events, tremor, and explosions. On 28 April an emission with a minor ash content rose 3 km and drifted W. Roaring was noted and lahars descended the La Pampa (NW) and Rea drainages.

Popocatepetl

During 22-28 April the seismic network at Popocatépetl recorded 25-91 daily emissions mostly consisting of water vapor and gas. Cloud cover sometimes prevented observations of the crater, although gas plumes and nighttime crater incandescence were noted daily. On 22 April an explosion at 01.21 produced diffuse gas and water vapor emissions. Explosions at 16.43 and 17.58 local time generated ash plumes. The Alert Level remained at Yellow, Phase Two.

Krakatoa

PVMBG reported that during 1 March-21 April diffuse white plumes rose 25-50 m above Anak Krakatau, although foggy weather often prevented observations. Seismicity continued to be dominated by shallow and deep volcanic earthquakes, as well as signals indicating emissions. The Alert Level remained at .

Sheveluch

During 17-24 April the lava dome extrusion onto Sheveluch’s N flank was accompanied by incandescence, hot block avalanches, and fumerolic activity. A thermal anomaly was detected during 16-18 and 23 April; cloud cover obscured views on the other days. The aviation code remained at Orange.

Figure 1; http://fineartamerica.com/featured/halemaumau-by-moonlight-grant-kaye.html

Figure 2; http://news.yahoo.com/image-asia-pyroclastic-flows-erupt-mount-sinabung-121702289.html