Category Archives: Africa

New Decade Volcano List; #7 Mountain of Greatness

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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…….

Mountain of Greatness – DVP # 7

Mount Fako, old lava flows. Wikimedia Commons.

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.

Geologic setting

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

Mount Manengouba Caldera.

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.

View from inside the caldera of Mount Bamboutos.

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.

Mount Oku with the caldera lake.

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.

Mount Ngaoundere with one of the for the Cameroon Volcanic Line so common phonolitic plugs.

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.

Annobón Island, a real tropical paradise where you can get down and dirty with your phonolite plugs.

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.

Now it is time to get really serious with the plugs. Pico Cão Grande on Sao Tomé.

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.

Beutifal shield crater lake with a shield in the background. Pico Basile volcano on Bioko Island.

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 Cameroon Volcanic Line showing the CVL, the CASZ and the Benue Through. Also visible is the horseshaped fault zone. Image taken from

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.

Benue Through

Eruption of Cameroon in 2000. Private photograph taken from Buea.

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 Hotspot

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.

Tomographic map of 25km depth. Do note the position of the African Superplume and keep track of it. No Visible signs of a hotspot here at CVL. Image made by DownUnder for Volcanocafé.

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.

Tomographic map of 25km depth. Do note the position of the African Superplume and keep track of it, also note how cold the two cratons are. No Visible signs of a hotspot here at CVL. Image made by DownUnder for Volcanocafé.

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.

Tomographic map of 25km depth. Do note the position of the African Superplume and keep track of it. No Visible signs of a hotspot here at CVL. Image made by DownUnder for Volcanocafé.

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.

Tomographic map of 200km depth. Do note the position of the African Superplume and keep track of it. No Visible signs of a hotspot here at CVL. Image made by DownUnder for Volcanocafé.

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.

Tomographic map of 300km depth. Do note the position of the African Superplume and keep track of it. No Visible signs of a hotspot here at CVL, instead the temperature is below average at the litosphere/adenosphere boundary, definitely not a Mantleplume nor a hotspot there. Image made by DownUnder for Volcanocafé.

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.

Mount Fako

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.

CARL (text) & DownUnder (tomography)

http://www.volcanocafe.org/science/mountain-of-greatness-dvp-7/

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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/

Today in Geological History; 17th January – Northridge and Nyiragongo

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The Northridge Earthquake 1994

At 4.30 am local time, the residents of the San Fernando Valley region of L.A were awoken by a shallow magnitude 6.7 earthquake. It is estimated to be one of the most costly natural disasters the state has faced causing up to 40 billon US dollars and killed over 60 people.

The earthquake struck along a fault line which was previously unknown off, the Northridge blind thrust fault. It produced the highest ever recorded ground motions at the time and literally threw many buildings off their foundations. It sparked greater mapping of the L.A fault systems so places could be better prepared for further destructive quakes in the future.

Some of the most dramatic pictures of the destruction came from the many freeways and interstates which suffered structural failure and/or collapse.

One of the most unusual outcomes of this earthquake was the outbreak of coccidioimycosis, or more commonly known as Valley fever. There were over 200 cases reported in the weeks after the quake and 3 fatalitites. Valley fever is a respiratory disease brought on by airborne spores of fungus. It is thought that landslides caused by the earthquake sent a cloud of the spores in the the air which the wind carried to surrounding areas.

 

Nyiragongo 2002

After months of increased activity at the stratovolcano in the DRC, a 13 km fissure opened along the southern flank of Nyiragongo in a matter of hours. The fissure reached all the way down to the town of Goma and Lake Kivu.

Over 400,000 people were evacuated from Goma and the surrounding area, many across the border to Rwanda. Despite these efforts 147 were killed, mainly from asphyxiation and some from collapsing buildings from volcanic tremors. About 4,500 buildings were destroyed in Goma and two-thirds of its airport left unusable as lava devoured the run ways.

When the flows reached Lake Kivu, due to the high gas emissions, a new fear was put in place. Similar to events at Lake Nyos 1986, there was a chance that the high emissions of carbon dioxide and methane could be stored in the lake waters and released lethal limnic eruption. Although this was not the case there have been numerous cases in the area around Nyrigongo of particularly children dying from asphyxiation due to random degassing of the volcano. An experimental syphon was put in place in 2001 to try to limit the amount of gas in the bottom waters, but it was not untill 2004 when an energy company wanted to harness the gas as a resource, did any really system come in to place to limit the risk of limnic eruption.

Nyrigongo is one of the 17 decade volcanoes, ones believed to pose greatest risk to human life. Caused by a mixture of rifting and hot spot activity, unlike many volcanoes of its kind, its lavas have an extreamly low silica content. Predominately melilite nephelinite, instead if more common more common basalts, it is extreamly fluid and can reach speed on average of 100 km/ph. It has also had a near constantlty active lava lake giving us the gentle reminder that it can fatally burst to life at any time.

 

1. Http://dart2.arc.nasa.gov

2. http://m.utsandiego.com/news/2014/jan/15/northridge-earthquake-anniversary-20/

3. http://www.unisdr.org/2006/ppew/info-resources/ewc2/UK/galerie/pg000057.htm

4. http://www.geo.arizona.edu/geo5xx/geos577/projects/kayzar/html/nyiragongo_volcano.html

Fogo

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As promised, this is a current catastrophe warrants its own post, especially as most of the world does not see it news worthy.

The islands of Cape Verde have become a popular destination for tourists off the coast of Africa. Their origins are volcanic;  as the African Plate moves across a hot spot. Although few of the volcanoes are believed to  extinct the island of Fogo which is thought to sit directly above mantle is rather active.

On November 23rd Pico de Fogo rumbled life again after laying in quiet almost 20 years. In an eruption true to typical hotspot volcanism, there were no huge blasts or billowing ash clouds sent rocketing in to the stratosphere, what there was was lava, volumes and volumes of basaltic lava. Moving at average speeds of just 10 m/ph basaltic lava is easily outrun and the villages like Portela and Bangueira were able to evacuate meaning little threat to human life. Does this therefore follow that there was no threat at all?

image

A month on the flow still advances completely devouring the towns of Cha das Caldeiras and Portela. Homes, schoools, businesses completely gone with former residents left helpless on the sidelines. Buildings in Bangueira are also being destroyed and the lava is heading towards other villages.

View image on Twitter

Yet what makes this situation worse is the lack of world support or even knowledge of the unfolding situation in Fogo. Sorry but to me peoples homes being destroyed, livelihoods lost is a big deal. Sadly Kim Kardashian’s naked backside seems to have more media interest than the poor people of Cape Verde.

I have mentioned on several posts that world ignorance to geological events is unbelievable. But what actually makes such news relevant to world media or aid?

Fellow member of the Open University community has a similar view and wrote as such for Science2o. “Does Ebola on mainland Africa and a typhoon in the Philippines mean that there really is no time for an event such as this in our mainstream news agenda? Or do we care about volcanoes only if there’s a chance of them inconveniencing our air-travel plans?”

I wonder how quickly this may change if people understood Fogo’s past and the danger that lays beneath the lava…..

The eastern flank of Fogo is scared from a collapse caused by an eruption around 40,000 years ago. The mass of rock, debris and volcanic material crashed in to the ocean causing a mega tsunami that make 2011’s Sendai disaster look like ripples in a puddle. On the neighboring island of Santiago, evidence of the catastrophic wave can be found over 100 m above sea level. It would of swept far inland on the west coast of Africa and decimated the coasts of Portugal and Spain.

The flanks of Fogo today are still not considered the most stable although it is thought we should not see another collapse in quiet some time, pending on future eruption styles. But the idea that this small volcano, which is currently seen as insignificant to the media, could threaten people on a global scale says so much about peoples ignorance to the planet we live on.

 

Rothery, D. http://www.science20.com/the_conversation/cape_verde_volcano_the_biggest_natural_disaster_you_arent_reading_about-150923

Today in Geological History; 21st August

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Apologies as this should have been publishes yesterday.

Lake Nyos, Cameroon 1986

Volcanism takes many shapes and forms, not all volcanoes eruption violently and explosively like Mount St Helens in 1980 neither do they all have a constant flow basaltic lava flowing from their vents such as Kilauea. Degassing can be constant at active volcanoes, poisonous gasses such as carbon dioxide and sulfur dioxide can seep out through the rocks even when all seems quiet. This can have devastating consequences on local population and wild life, but very few times has it been quiet so fatal as the summer on 1986 in Cameroon.

Lake Nyos is a crater lake which lays in the Oku Volcanic Field at the northern end of the Cameroon Volcanic Line. This area is known to degas large quantities of varying substances most of which dissipates in to the atmosphere. However, water is able to dissolve and store quite high quantities on CO2, especially the cold bottom waters of a water body such as Lake Nyos. 

lake-nyos-21. Lake Nyos in 1986 a week after the incident.

On 21st of August 1986 at approximately 9.30pm local time, a cloud rich in CO2 swept the surrounding area from the lake. Over 1700 people were killed as well as thousands of cattle and other wildlife. Air has to be just 15% CO2 for people to loose consciousness and have difficulty breathing; the cloud is believed to have had a much higher concentration then that. People simply fell asleep never to wake up, dying of asphyxiation.

081223.AF_.villager2. Locals lost every thing with few livestock surviving.

There are several theories to the exact cause of the gas cloud. Firstly was the idea of a ‘carbon dioxide eruption’ from the volcanic system; it literally burped out great amounts of the gas in one go, so much so that it couldn’t be held in the water and seeped in to the atmosphere and down to the surrounding villages. The second theory was based on an event two years previous in the August of 1984 at Lake Monoun. A landslide stirred the water of the lake causing ascent of the carbon rich bottom waters. No longer under the pressure of the depths the CO2 began to exsolve (bubble out of solution) and was release in mass in to the air. Unlike at Nyos this was a smaller incident only claiming 34 lives but it gave scientific insight to what occurred two years later. There were no signs of any landslide on the banks of Nyos in August on 86′ however there had been heavy rainfall. Rain waters would have been much colder, and therefore denser, than the lake water causing a convective overturn. Again as bottom waters rose the dissolved gases would have been released with catastrophic effect.

What ever the cause, a painful lesson was learned and in 2001 a large polyethylene pipe was placed in to Lake Nyos, with a second being put in place in 2011, to siphon water continuously from the lower layers to the surface so there is never an excessive build up of CO2.

1. http://science.howstuffworks.com/environmental/earth/geophysics/lake-nyos1.htm accessed 20/08/14

2. http://www.emigennis.com/2014/04/06/lake-nyos-disaster-reference-photos/ accessed 20/08/14