Today marks the 130th anniversary of Tarawera bursting back to life after 500 years of sleep. It was one of New Zealand’s largest eruptions in recent history and killed up to 150 people making it the countries most deadly since the arrival of the Europeans.
Tarawara was last active in 1315 and is believed to have had a great hand in the Great Famine of 1315-137 throughout Europe. In 1886 the mountain gave little warning of up coming events. On June 1st a series of waves were recorded on the surface of Lake Tarawera suggesting seismicity in the area although no one reported feeling quakes and there where no seismometers at this time. Tourists claimed they saw a phantom canoe floating across the waters with Maori warriors on board. Although there were multiple accounts on the sighting many believed it was simply a rogue wave caused by increased seismicity, tribal elders at Te Wairoa however claimed that it was a waka wairua (spirit canoe) and was a portent of doom.
All was quiet again in the following days and people though little of the complex. Many geologists at the time didn’t even consider the edifice to be active due to the lack of solfataric or fumarolic activity in comparison to New Zealand’s other volcanoes.
At 2am local time on June 10th this all changed. Locals where awoken by large tremors shortly followed by explosions heard as far away as Blenheim over 500 km to the south. by 2.30 all three peaks of Tarawera were eruption with fire fountains lighting up the pitch black, ash filled skies. The eruption began to the northeast side and spread rapidly along a fissure from Tarawera to Lake Rotomahana into the Waimangu Valley. The eruption was believed to be caused by a series of basaltic dikes which rose from depth and intersected the very active hydrothermal system under Tarawera and Lake Rotomahana, causing rapid steam/magma explosions, driving the plume that was observed and creating, by some accounts, fire fountains as tall as 2 km which explains the high explosively of a basaltic eruption.
The darkened skys were seen as far as Christchurch and was catapulted in the stratosphere where it lingered effecting climate for at least a year. The ash fall from the eruption – called locally the “Rotomahana Mud” – can be found into the Bay of Plenty almost 40 km away. This tephra covered 15,000 km2 over the North Island and over 4,500 km2 of the area with at least 5 cm of tephra.
The eruption itself produced at least 1.3 km3 of tephra (~0.7 km3 of dense rock equivalent), likely at a rate of higher than 6 x 104 m3/s. It also produced a base surge that travelled over 6 km from the craters moving 40 m/s and were large enough to top hills that were 360 meters tall which buried several Maori villages.
The Buried Village Rotorua is now a popular tourist destination often branded New Zealand’s answer to Pompeii. As well as the human impacts it also buried the Pink and White Terraces.
Today marks the 25th anniversary of the pyroclastic flow from Mount Unzen which claimed the lives of 43 people.
Mount Unzen is actually several over lapping volcanoes on Japan’s island of Kyushu. It was the cause of Japan’s largest ever volcanic disaster in 1792 when a lava domed collapsed and caused a mega tsunami which killed nearly 15,000 people. After this even the volcano lay silent until beginning to stir in 1989.
Seismic swarms began in the November of 89 about 10 km west of the summit and gradually migrated eastward until the first phreatic eruption a full year later in November 1990. By May 20th 1991 fresh lava began to flow from the highly inflated summit area prompting the evacuation of almost 12,000 locals.
The threat of another eruption to the scale of 1792 brought journalists and scientists alike flocking to the surrounding area to monitor the activity of Unzen and its potential threat. Sadly this curiosity resulted in the deaths of 43 when on June 3rd activity peaked due to a possible lava dome collapse. This sent a huge pyroclastic flow surging down its flanks and funnelled in to a valley point in the direction where volcanologists and journalists had set up a base at what was thought to be a safe distance, over 4.5 km, from the summit.
Activity continued well in to 1995 and over 10,000 pyroclastic flows were recorded over this period. By the end of the eruption a new lava dome was in place 1.2 by 8 km wide. Its volume was approximated at 0.1 cubic km. In total, about 0.21 cubic km of plagioclase-phyric dacite magma was erupted over the course of the eruption at peak effusive rates of 7 cubic metres per second in 1991. Over 2000 buildings were destroyed by these flows in Shimabara City alone. Matters were further complicated between August 1992 and July 1993 when heavy rains caused multiple lahars destroying a further 1300 homes along the Mizunashi and Nakao Rivers, requiring the sudden evacuation of several thousand residents.
Mount Unzen has been placed on the official decade volcano list and is one of Japan’s most highly monitored areas.
Maurice and Katia Krafft
The Krafft’s were French volcanologists and soul mates who met at the University of Strasbourg. Their love for volcanology almost reviled their love for each other. The specialized in documenting eruptions as best and often as close as possible, their end was almost inevitable.
Their most famed contribution was the documentation of Nevado del Ruiz which when shown to the Phillipine president Corazon Aquino who was then convinced to evacuate the area surrounding Mount Pinatubo before its catastrophic 1991 eruption almost certainly saving hundreds if not thousands of lives.
Over a 20 year period, when volcanology was still a relativity young science, the married couple documented hundred of eruptions. They fillmed over 300 hours of footage, took thousands of photos and published multiple books.
While in the Philippines during Pinatubo’s early stages, Maurice was interviewed by a local news agency where he told the journalist “I am never afraid, because I have seen so much eruptions in 23 years that even if I die tomorrow I don’t care.” From here they flew out to Japan where activity was picking up at Unzen. The pair perished together when they were overcome by the pyroclastic flow on June 3rd.
Harry was an American volcanologist who although was based at USGS was funded by outside organisations. He specialised in volcanic debris flows and was closely involved with research on St Helens with his doctoral thesis ‘Rockslide-debris Avalanche of May 18, 1980, Mount St. Helens Volcano, Washington‘ being recognised as a leading paper on the event.
Glicken cheated death on St Helens as he was meant to be the volcanologist on duty May 18th however swapped with his then mentor David Johnston who was killed by the blast.
Sadly I awoke this morning to the news Mount Sinabung in Northern Sumatra, Indonesia had claimed the lives of three farmers working in the fields by the Gembar Village. This figure has since risen to 7 and is feared to continue to rise with several more critically injured and the Red Cross and army looking for further victims.
Mount Sinabung has been in a near constant state of eruption since late 2013. Pyroclastic flows sweep down its flanks on a regular basis which has lead to 4 km exclusion zone being enforced around the summit. On February 1st 2014 people were killed by one such pyroclastic flows.
About 10,000 people have been displaced by activity at the volcano which has been on the highest state of alert for well over a year. Sadly the volcano is positioned in a relatively poor and over populated area of the world, many people have little choice but to continue to farm on the volcanoes fertile flanks. Officials have struggled to keep the people to stick the ‘red’ exclusion zones and it is unclear how many people were on the mountain at the time of the recent activity.
Head of the National Disaster Mitigation Agency (BNPB) Willem Rampangilei has instructed Karo Regent to take quick measures to vacate the red zones (Gamber village, Simpang Empat district and Karo Regency) but they know that this is easier said then done. The pyroclastic flows caused by partial collapses of the growing lava dome occurred in a series at 14:28, 15:08 and 16:39 local time on Saturday. Rescue attempts went through the night and in to Sunday morning. An ash column remained for hours, towering over the area darkening the skys and hampering the search operation.
The pyroclastic flow captured here to the left happened only a week ago on May 16th showing the power and regularity of such activity. On May 9th a lahar swept through Kutambaru near the Lau Barus River killing 1 and leaving one person still missing now also presumed dead.
Sinabung lay silently for nearly 400 year until springing back to life back in 2010. It has now killed at least 25 people since its rousing. Volcanism on the island of Sumatra is caused by the subduction of the Indo-Australian plate beneath the Eurasian plate along the Sunda Arc which creates the andesitic-dacitic composition magmas which are prone to such explosive activity. Sinabung sits just 25 miles north-east of the Toba Super Volcano caused by the same tectonic motion.
In the past week the Japanese Island of Kysushu has be ravaged by earthquakes.
Japan is a highly seismic area with noticeable quakes in some areas occurring nearly daily. But things began to escalate for the Kyushu region on Thursday night when a magnitude 6.5 quake brought several buildings down. As rescue efforts began the region had two more huge after shocks during the night, one over Mg 6 and the other > Mg 5. By midday Friday the death toll stood at 9 with over 800 injured and although the aftershocks kept coming many >Mg 4 people were still being pulled from the rubble. Sadly these events were quite possibly a precursor to something larger.
At 01.25 local time (15.25 GMT) a Mg 7.3 struck just north of Kumamoto just kilometers from the large earthquakes which had already occurred. Much of the seismicity in the Kyushu region is related to the subduction of the Philippine Sea plate at great depth. However this series of earthquakes have occurred at very shallow depths several hundred kilometers northwest of the Ryukyu Trench. They have been cause by strike-slip faulting within the Eurasian plate.
So far 22 more people have been reported dead but this is expected to rise in the coming days with at least 80 people known to betrapped in rubble. 11 of which are trapped in a Tokai university apartment in the town of Minami Aso.
The shallowness of the earthquakes means damage to the surface is high and it is not just collapsing building which are a hazard. People have fled the area down stream of a dam which collapsed soon after the earthquake. Landslides in the area have taken out roads and power lines and with heavy rain anticipated over the coming days JMA have advised mudslides will be a huge problem for rescuers.
The seismic problems of Kyushu may have also set in motion another geohazard in the form of Mt Aso. Yesterday one of my favorite volcanology bloggers Eric Klemetti tweeted “Quite a few volcanoes on Kyushu and these earthquakes have been centered near Unzen, Aso, Kirishima. This is NOT to say these earthquakes will trigger any eruptions, but could be worth watching over the next year.” Several hours late JMA reported a small scale eruption at Aso. Smoke plumes have migrated 100 meters above the summit and it is not yet clear if the activity is magmatic (caused by movement of magma towards the surface) or phreatic (steam explosion caused by heating of groundwater).
Eruptions and earthquakes do not always come hand in hand but each one can contribute to the other or not at all depending on the circumstances. One indication a volcano is about to erupt is volcanic tremors; these low frequency earthquakes are usually caused by the migration of magma or changes to magma chamber. Although they are rarely higher than a magnitude 4. On the other side large earth quakes can cause faulting in bed rock which allows magma to exploit a new weakness and find a path to the surface it previously could not intrude on. The same can happen for ground water with faulting caused by a quake allowing it to seep in to geothermal areas it previously did not have access to due to the impermeability of the rock. When earthquakes hit volcanic regions volcano observatories always keep a closer eye on vulnerable or highly active volcanoes as a precaution but it is not always needed.
The Aso Caldera complex has one of the world’s largest calderas. It is comprised of a 25 km north-south by 18 km east-west Caldera and a central cone group comprised of Mt. Neko, Mt. Taka, Mt. Naka, Mt. Eboshi, and Mt. Kishima. Mt Naka where the eruption has just taken place is the most active with its most recent eruption taking place last October. Although much of Aso’s activity in the past century has been relatively small it has had a violent history with at least 4 VEI 7 events in the past 300,000 years.
It’s is not clear whether the earthquakes in the past few days did trigger the current current eruption but JMA are keeping a close eye on the situation and I will update this page as I know more.
Today 416 years ago South America experienced its most explosive eruption in historical times. The unassuming Huaynaputina volcano sits in southern Peru just 26 km of Ubinas, the countries most active volcano. Unlike its 5672 m neighbour, Huaynaputina has no distinct topographic elevation and lays inside a 2.5 km crater leading many to believe it was just a mountain caused by other forces. Laying in the Andean Volcanic Belt where the Nazca Plate subducts under the western edge of the South American Plate it is situated on the rim of the Rio Tambo canyon further camouflaging it to the untrained eye.
The sleeping giants last eruption was in February 1600. Reaching an impressive VEI 6, it was the biggest eruption of the past 2000 years.
Details of the eruption were captured beautifully by Fray Antonio Vazquez de Espinosa a Spanish monk travelling through Central and South America at the time. Days before the eruption booming noises were heard from the vicinity and steam was seen seeping from the volcano. Locals began to panic, preparing young girls for sacrifice to appease Supay the god of death who people believed was angry at them and causing the mountains behaviour. February 15th marked a strong increase in activity with tremors becoming stronger and more frequent, many began to leave the area fearing something bigger was coming.
At roughly 5 P.M. on February 19th, Huaynaputina erupted violently catapulting ash high in to the stratosphere. Pyroclastic flows sped down all sides of the volcano, to the south mixing with the waters of the Rio Tambo river causing devastating lahars. Within just 24 hours, Arequipa was covered with 25 centimetres (10 in) of ash. Ashfall was reported 250–500 kilometres (160–310 mi) away, throughout southern Peru and in what is now northern Chile and western Bolivia. It is thought that more than 1500 people were killed by the eruption its self although with little record of populations at the time the figure varies between sources. 10 villages were completely buried by ash and regional agricultural economies took 150 years to recover fully.
It was not just South America which was effected by the eruption. Ice cores recorded a spike in acidity at the time indicating a phenomenal amount of sulphur dioxide was released. Effects on the climate right around the Northern Hemisphere (Southern Hemispheric records are less complete), leading to 1601 being the coldest year in six centuries, leading to one of the worst famines ever recorded in Russia. In Estonia, Switzerland and Latvia, there were bitterly cold winters in 1600–1602 leading the deaths of hundreds; in 1601 in France, the wine harvest came late and in Germany production of wine collapsed completely. In Japan, Lake Suwa had one of its earliest freezings in 500 years and even China recorded peach trees blooming late.
An eruption of this scale in the populated Peru would be devastating so close watch is kept on Huaynaputina and its more active neighbours.
For years a major thing on my bucket list was to swim in a crater lake, which as the name suggests is a body of water formed in a volcanic crater or caldera. Luckily I got to tick this one of when I visited Nicaragua last year and swam in the blissfully warm Apoyo Lagoon, but of course this only appealed to my addictive nature and made me dream about going one better…how about a crater lake formed by a super eruption. When my friend told me she was off travelling for a few months and her first port of call would be New Zealand, I decided she could live my dream for me on this one and I straight away advised her to head to Lake Taupo. Of course to any one without local knowledge or a familiarity with historic eruptions, this would not be of any significance. To be honest neither would me telling them I want to go swim in a random lake in New Zealand. So I decide to write a peace on one of the largest eruptions in the past 70,000 years to explain just why it is so important.
With a surface area of 616 square kilometres (238 sq mi), it is the largest lake by surface area in New Zealand and the second largest freshwater lake in Oceania. Now it’s a popular tourist destination, an area of true natural beauty, but this tranquil lake was born from a violent even which occurred roughly 26,000 years ago.
The Taupo volcanic zones spans a hug area in North Island 350 kilometres (217 mi) long by 50 kilometres (31 mi) wide. Mount Ruapehu stands 2797 high and marks its southern limits, while a submarine volcano, Whakatane volcano, 85 kilometres (53 mi) beyond White Island is considered it’s north-eastern. Several volcanoes in the zone are still very active with Ruapehu and Tarawera causing New Zealand’s most deadly eruptions in the past few centuries (both events killing around 150 people each). None of these small events come close to the Taupo volcano itself after which the zone is named. The zone is caused by east-west rifting within plate the at a rate of 8mm per year, slowly pulling the Northern Island apart.
Taupo’s last eruption is referred to as the Hatepe eruption and has be dated at roughly 180 AD was a VEI 7 making it one of the largest in the past 5,000 years. It coincided with reports as far away as Rome and Northern China of brilliant red skyies and disruption to climate for several years. Haptepe spewed more material in to atmosphere than several of the largest eruptions of this century combined, but still it was nothing compared to the event which form the Taupo caldera and in turn Lake Taupo; the Oruanui eruption.
The Unit as the level of the volcanologists feet is an exposure of an unwelded pyroclastic flow deposit from the Oruanui eruption. The light- coloured air fall pumice are from varying eruptions between Oruanui and the uppermost layer of deposits which were laid by the Hatepe eruption.
Its hard to imagine what the Northen Island looked like before the Oruanui eruption 26,500 years ago with out the gapping hole that is Lake Taupo at its heart. The eruption released an estimated total of 1,170 km3 (280 cu mi) of material, a VEI 8 eruption making it the largest eruption of the past 70,000 years. It effected climate world wide for decades, many people saying it had a helping hand in the last glacial maximum. The effects are hard to comprehend when the largest volcanic eruption in human times was only a fraction of the size.
The eruption caused the Taupo magma chamber to collapse on its self creating the vast caldera which today Lake Taupo occupies just over two thirds of. Ash fall deposits from the eruption have been documented over 1000 km on Chatham Island showing the intensity of the blast. An event like this would decimate modern day New Zealand quiet possibly leaving no survivors on the Northern Island if not enough warning was given. Luckily though all is peaceful and scerene on the shores of the Great Lake and no threat appears to be imminent. That said Taupo still shows us gentle signs of the power beneath with its Craters of the Moon tourist attraction filled with steam vents and mud pools as well as numerous hot springs.
When people ask me why I study volcanology when the risk is “minimal” to human life in comparison to say earthquakes or flooding, this is a prime example which shows how little people know about what our planet is capable of. So Ginge, I hope you enjoy your trip and now understand a little more why Taupo is one part of your adventure I sincerely wish I was there!
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
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.
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.
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!
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:
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.
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.
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)
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).
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.”
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 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?
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.
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.
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.
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’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.
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%).
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 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!!!
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!
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.
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.
Sadly the other week the awesome VolcanoCafe sight came under attack by an old member of the admin and was decimated. Luckily for all of us avid readers it can now be found on http://www.volcanocafe.org Now it is back up and runnin Carl and Henrick have managed to throw up an unexpectid number 7 for their new decade volcano list. Introducing Mount Cameroon…….
Few volcanoes on the planet represent such an awesome sight as the majestic Mount Cameroon. It stretches from the edge of the Atlantic at Bakingili Beach and reaches an astounding height of 4040 meters. Due to its prominence it is regularly dusted with snow at the top.
Mount Cameroon, or as I am used to calling it, Mount Fako, is the only volcano to date that I have worked professionally with as a geophysicist. As volcanoes go it is somewhat of a “terra incognita”, and to be quite frank, most that has been written about the volcano is just not correct. So, there is an ample chance here to set a few things straight, do some real science, and also put the limelight on one of those volcanoes of the world that is both highly dangerous and completely unmonitored.
To understand Mount Fako we first must start with the geologic setting, and also come to terms with the geologic timescale of West African Volcanism. There are 3 distinct geological features that we need to contend with as we speak about Mount Fako.
The Cameroon Volcanic Line
The first one is the Cameroon Volcanic Line, it consists of 4 volcanic Islands, 2 large seamounts, Mount Fako itself, Manengouba, Bambouto, The Western Highland with Mount Oku, Ngaoundere, Mandara and Biu. Volcanism in the Cameroon Volcanic Line spans a time period of 49 million years and contains two distinct periods.
The first period consists of magmatic domes and maars, most of them are heavily eroded today and requires specialized knowledge to find. This period ended about 33 million years ago and can be seen as a proto-volcanic phase.
The second period started 32 million years ago at Mandara and Mount Oku. The ensuing volcanism is highly programmatic and follows a pattern where the volcanoes are born through large scale basalt eruptions creating layers between 50 and 600 meters thick. After that comes a period of trachytic lava with minor rhyolitic ignimbrites, after that comes a large caldera event with subsequent dyke formations and phreatomagmatic eruptions of diminutive scale.
The eruptive phases of the volcanoes spans from millions of years to tens of millions of years. There is no good explanation to why the basaltic eruptions during a fairly short time switch to highly explosive volcanism. My suggestions is that the large basalt flows necessitate large volume magma reservoirs that over time fills with residue from earlier eruptions and also that the magma reservoirs becomes inundated with stale base rock low in volatiles.
The formation of Cameroon Volcanic Line has erroneously been attributed to a hotspot or mantleplume. And to the naked eye there seems to be a telltale track of volcanic islands and volcanoes. There is just a problem, there is definitely no hotspot or mantleplume to be had. I will though get back to this later on.
Let us start at the Northeast and work our way down to Mount Fako. The first volcano we stumble upon is Biu, very little is known about the volcano except that it morphologically follows the normal composition for a CVL volcano and that is started its activity less than five million years ago.
To the southeast comes the 32 million year old volcano of Mandara with an unstudied volcano due south. Further southeast of that unstudied volcano is the massive caldera of Nagoundere.
The group above is a distinct group of its own, not due to being morphologically different; instead they sit on a different rift system than the rest of the volcanoes. This rift system is roughly horseshoe shaped and transects the Central African Shear Zone that is home to the volcanoes below.
Now it is time to continue with the Western Highlands that consists of two main volcanoes. The northernmost of those is Mount Oku that was active 31 to 22 million years ago before it went caldera forming Lake Oku. Southwest of Mount Oku we find the massive caldera of Bambouto that was active between 21 and 14 million years ago.
Next in line is the 1 million year old active volcano of Manengouba that is situated northeast of Mount Fako. It is a part of the Fako volcanic zone but is a younger and distinctly separate volcano. What makes Manengouba so interesting is that it took less than 1 million years before it went caldera.
If we for now skip Mount Fako itself and jump to the other end of the CVL we find the miniscule volcanic island of Annobón and its volcano Pagalu. This diminutive Island formed during an unusually short volcanic period that started 5 million years ago and lasted less than 1 million years.
Next in line is Sao Tomé that is one large shield volcano. It started to form 13 million years ago and the volcano is still believed to be active due to the young cinder cones situated on the southeast side of the island. It is also well known for the Pico Cão Grande volcanic monolith.
To the northeast of Sao Tomé we find the island of Principe that erupted from 31 million years ago to 14.7 million years ago.
The next island is Bioko that is housing no less than 3 major shield volcanoes that have been active historically. Volcanism here started 1 million years ago and eruptions occurred last in the 19th century.
Central African Shear Zone
All of the volcanoes from Pagalu up to that peskily unstudied volcano is situated on the CASZ, through that unstudied volcano runs the previously mentioned horseshoe shaped fault zone.
The CASZ formed around 640 million years ago and was volcanically active around that period. Previously western scientists believed that the CASZ was tectonically inactive until an M5 earthquake occurred and was monitored on a temporary seismometer. Local sources have though always stated that large earthquakes happen frequently along the shear zone, especially during eruptive phases where houses commonly have been leveled by the intense seismic activity.
The CASZ was volcanically active both 640 million years ago and also 130 million years ago during the break up of Pangea. One should note that the 3 active periods do not rule out smaller scale volcanism in between. As such the CASZ is the oldest volcanic feature on the planet that is still active.
The CASZ used to continue in the form of the Pernambuco Fault in Brazil, but as some people have noticed, the breakup of Pangea occurred and the Shear Zone ended up divided across two continents by a sizeable ocean.
At the same time as the single largest eruptive episode started at Paraná-Etendeka with both trap formations and the largest explosive eruptions on record the West African Craton and the Congo Craton started to separate at what is today the Benue Through.
Volcanism at Benue Through started prior to the Paraná-Etendeka event at 149 million years ago and continued for roughly 100 million years.
As the breakup of Pangea was completed the Benue Through separation of Cratons reversed and the Through started to close up, that created a heavily folded zone adjacent to the CASZ. I would seriously try to remember this feature in your mind as I get back to the hotspot and mantleplume issue.
The reigning theory for the volcanism on the Cameroon Volcanic Line is that it is created by a hotspot that is travelling in an ENE direction. Only problem is that the time record does not support this at all. To be quite frank, the pattern of age of the volcanic centers is entirely random. Let us repeat the ages from north to south. 5, 32, unknown, 11, 31, 21, 1, 3, 1, 31, 14 and 5. Either I have grown dimwitted or there is just not any time sequence that is associated with a hotspot track 1 600 kilometers long.
Some have tried to save this by surmising that there is another hotspot there and they also favor to put in influence from the Saint Helena Hotspot in the mix. It still does not blend very well with reality.
So, if the time does not indicate a hotspot, what does? Well, the temperature of the erupted magmas is quite enigmatic. The volcanoes have erupted varied temperature magmas with the heat record at 1 338C and the coldest at 1 106C with a medium temperature of 1 280. That would put it at 220C below the temperature of the Hawai’i hotspot and en par with the Icelandic Hotspot. As such that would be a fairly cold hotspot, but those exist as we know from Iceland.
Only problem is that the hotspots of Iceland, Hawai’i and the African Plume are caused by upwelling from deep within earth and all 3 of those are clearly visible when you create tomographic charts of the mantle.
A tomographic chart shows anomalies in the speed at which sound travels after an earthquake. The most clearly visible such entities are the Icelandic Hotspot and plume upwelling and the African Plume residing under Eastern Africa. Those can be seen very deep indeed.
Problem is just that if we go and look at the CVL we see nothing as such, actually we even find inverse anomalies at depth showing the area to be slightly cooler than expected.
The next theory is that the Benue Through is causing a localized upwelling of material from below the LAB (Lithosphere-Asthenosphere Boundary). Only problem is that this is not evident from the tomographic maps either.
This leaves us with a conundrum. We only know that there is no hotspot causing the volcanism. We also know that the volcanism is extremely extended in time.
Volcanism is caused either by hotspots, spreading rifts like the MAR or subduction caused melt. We know that for about 50 million years there was spreading rift volcanism going on adjacent to the CVL at the Benue Through, we also know that this started after the CASZ volcanism. We also know that there historically has been no subduction going on there. Sooner or later subduction in the area will start, but we are not there quite yet geologically speaking.
We are here left with a 640 million year old riddle regarding volcanism. Either we are missing something, or we have a fourth form of volcanism going on at the CVL. Sadly the CVL and Mount Fako is highly understudied. This is the first reason that Mount Fako should be on the new Decade Volcano Program.
Even though it is sited as being a stratovolcano Mount Fako is actually a fissure row of volcanic craters. In some respects it reminds of an effusive cousin of Iceland’s Hekla volcano in shape. Eruptions at the volcanic fissure line started 3 million years ago with large scale basalt flows that built up an elongated shield. As volcanism continued with shorter lava flows the sides have grown increasingly steeper until a steep sided elongated hull like shape formed.
As volcanism progressed the lava flows has grown increasingly volatile rich and eruptions often take place at 2 or more places. One of the sites will be high up on the volcano and will be explosive in nature and further down the fissure there will be an entirely effusive eruption causing lava flows that often reach down to the Atlantic Ocean.
The eruptions span between VEI-2 and VEI-4 with VEI-2 sized eruptions being the by far most common type.
During eruptions the volcano becomes highly seismic with extensive and intense earthquake activity that often affects the capital of the Southwest Region Buea heavily with raised houses and deaths occurring. Normally residents of Buea are forced to sleep outdoors during eruptions to not risk that their houses cave in on them.
The lavas erupted are bimodal with basalts as the main component, but the other component are trachytes and phonolites signifying a volcano containing more evolved lavas in an intermediary stage. The sheer size of the 1 400 cubic kilometer volcano, the unstable flanks and the evolving magmas, point to a volcano nearing its end stage.
If we compare Mount Fako to its post caldera brethren to the northeast we can see that they reached about the same size before they went caldera. The volcano does though not yet hold evolved enough magmas to form ignimbrite flows.
The main forms of hazard are through seismicity and flank collapses. For flank collapses the cities of Buea and Limbé are in the strike distance. The gravest danger of this volcano is though not through an explosive eruption.
Instead the gravest risk is that a large basalt flood event will occur like the one that was potentially witnessed by Hanno the Navigator 450 BC. Another large effusive eruption would not kill people directly, instead gas content and destruction of cities and farms would cause the death toll.
Mount Fako is today not monitored at all. There is no active Seismometer, no GPS, no Inclinometer. Instead the park rangers are tasked with observing what is going on visually and forward the information to anyone interested in knowing it.
Together with the risk to the large local population and the scientific conundrum that Mount Fako poses it clearly merits to be placed at place number 7 on our proposed new Decade Volcano Program.
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;
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!