GeoLog

Geochemistry, Mineralogy, Petrology & Volcanology

Imaggeo on Mondays: Pyroclastic flow, Montserrat

Below the warm and tranquil waters of the Caribbean, some 480 km away from Puerto Rico, the North America Plate is being subducted under the Caribbean Plate. This has led to the formation of the Lesser Antilles volcanic arc; the result of the formation of reservoirs of magma as fluids from the down going North America Plate are mixed with the rocks of the overlying Caribbean Plate.

The continued magma generation is expressed violently at the surface on Monserrat Island, which has been the subject of extensive scientific scrutiny since the mid-1990s. This is all because of Soufrier Hills volcano, a Pele’ean type lava dome complex. This means that rather than explosive eruptions taking place, very viscous lava is slowly erupted from the volcano’s vent. The lava is so sticky and gooey that instead of flowing away, down the flanks of the volcano, it accumulates in the vent area and forms a large plug. Lava domes come in a range of shapes and sizes, in the case of Soufrier Hills, it tends to be circular and quite spiky.

Just because the eruptions on this Carbbien Island aren’t generally as spectacular, as for instance at Mt Etna in Italy, they are no less deadly! A common hazard associated with the building up of a dome by the continued accumulation of volcanic material means they can become dangerously unstable and collapse. The volcanic material careers down the flanks of the volcano in the form of pyroclastic density currents (PDCs). The largest such collapse ever observed took place in July 2003 and numerous smaller flows have occurred since. One rather large collapse happened in early 2010, when the dome atop Soufrier Hills had grown to be 1150 m asl (above sea level). After a period of unrest which started in late 2009 and was characterised by seismicity and extrusion of lava from the vent, there was a catastrophic dome collapse in February which reduce the summit height by almost 100m!

Pyroclastic flow, Montserrat. Credit: Alan Linde (distributed via imaggeo.egu.eu)

Pyroclastic flow, Montserrat. Credit: Alan Linde (distributed via imaggeo.egu.eu)

“The photo is taken from a spot at the water’s edge (just behind me) that was previously about 200 m out to sea. A PDC pushed the shoreline out by as much as ~600 m,”

says Alan Linde, who took this photograph of the smoking black landscape in April 2010.

Alan and the research team from the Department of Terrestrial Magnetism (DTM, Carnegie Institution for Science) have been involved with studying Soufrier Hills since 2003. By installing a network of very sensitive instruments in small shafts dug into the ground in and around the volcano, known as borehole strainmeters, they can measure changes in the size and volume of the ground as a result of dome collapses and explosive eruptions.

 “One of our borehole sites, very close to the coast, was almost destroyed by the hot ash. There is a clear change (from before to after the flow) in the tidal signals recorded by that site because an area of ocean loading has been removed as a result of the ash filling in and moving the coastline. The volcano is behind the small mountains, obscured by cloud.”

 

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

 

Imaggeo on Mondays: An explosive cloud

Imaggeo on Mondays: An explosive cloud

One of the world’s most volcanically active regions is the Kamchatka Peninsula in eastern Russia. It is the subduction of the Pacific Plate under the Okhotsk microplate (belonging to the large North America Plate) which drives the volcanic and seismic hazard in this remote area. The surface expression of the subduction zone is the 2100 km long Kuril-Kamchatka volcanic arc: a chain of volcanic islands and mountains which form as a result of the sinking of a tectonic plate beneath another.  The arc extends from Hokkaido in Japan, across the Kamchatka Peninsula, through to the Commander Islands (Russia) to the Northwest. It is estimated that the Pacific Plate is moving towards the Okhotsk microplate at a rate of approximately 79mm per year, with variations in speed along the arc.

There are over 100 active volcanoes along the arc. Eruptions began during the late Pleistocene, some 126,000 years ago at a time when mammoths still roamed the vast northern frozen landscapes and the first modern humans walked the Earth.

Many of the volcanoes in the region continue to be active today. Amongst them is Karymsky volcano, the focus of this week’s Imaggeo on Mondays image. Towering in excess of 1500 m above sea level (a.s.l), the volcano is composed of layers of hardened lava and the deposits of scorching and fast moving clouds of volcanic debris knows as pyroclastic flows. You can see some careering down the flanks of the volcano in this image of the July 2004 eruption. The eruptive column is the result of a

“strong Vulcanian-type explosion, with the cloud quickly rising more than 1 km above the vent. The final height of the eruption cloud was approximately 3 km and in the image you can clearly see massive ballistic fallout from multiple hot avalanches on the volcanoes slopes,”

explains Alexander Belousov, a Senior Researcher at the Institute of Volcanology and Seismology in Russia and author of this week’s photograph.

 

USGS map of the Kuril-Kamchatka trench, showing earthquake locations and depth contours on downgoing slab. Credit: USGS, USGS summary of the 2013 Sea of Okhotsk earthquake, via Wikimedia Commons.

USGS map of the Kuril-Kamchatka trench, showing earthquake locations and depth contours on downgoing slab. Credit: USGS, USGS summary of the 2013 Sea of Okhotsk earthquake, via Wikimedia Commons.

If you pre-register for the 2015 General Assembly (Vienna, 12 – 17 April), you can take part in our annual photo competition! From 1 February up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

Imaggeo on Mondays: A Patagonia landscape dominated by volcanoes

Patagonia Landscape. Credit: Lucien von Gunten (distributed via imaggeo.egu.eu)

Patagonia Landscape. Credit: Lucien von Gunten (distributed via imaggeo.egu.eu)

Imagine a torrent of hot and cold water, laden with rock fragments, ash and other debris hurtling down a river valley: this is a lahar. A by-product of eruptions of tall, steep-sided stratovolcanoes, lahars, are often triggered by the quick melting of snow caps and glaciers atop high volcanic peaks.

The history of the Ibañes River and its valley, in southern Chile, are dominated by their proximity to Hudson volcano (or Cerro Hudson, as it is known locally). Located in the Andean Southern Volcanic Zone, the volcano has an unsettling history of at least 12 eruptions in the last 11,000 years. That equates to a major eruption every 3,800 years or so! The volcano has a circular caldera, home to a small glacier and is neighboured by the larger Huemules glacier.

One of the most significant eruptions occurred in 1991. It is thought to be one of the largest eruptions, by volume, of the 20th Century. At its peak, the eruption produced an ash plume thought to be in excess of 17km high, with ash being deposited as far away as the Falkland Islands. The initial eruptive phase was highly explosive. Known as phreatomagmatic eruption, hot and gas rich magma mixed with ice and water from the glacier on the summit of Mt. Hudson. As the eruption progressed, a period of sustained melting of both the caldera glacier and Huemules glacier began. The result of this was a 12 hour period of persistent lahar generation, with volcanic debris laden torrents racing down the Ibañes valley and its neighbours.

Fast forward to 2009 and the effects of the eruption of 1991 are still visible in the Patagonian Landscape. Lucien von Gunten photographed the inhospitable ‘Bosque Muerto’ (Dead Forest), in the Ibañes valley. The accumulation of the lahar deposits and the ash fall from the eruptive column clogged up the Ibañes river and valley killing a large proportion of the local flora and fauna. The ‘Bosque Muerto’ remains a stark reminder of the devastating effects of the 1991 eruption.

Reference

David J. Kratzmann, Steven N. Carey, Julie Fero, Roberto A. Scasso, Jose-Antonio Naranjo, Simulations of tephra dispersal from the 1991 explosive eruptions of Hudson volcano, Chile, Journal of Volcanology and Geothermal Research, Volume 190, Issues 3–4, 20 February 2010, Pages 337-352

 

If you pre-register for the 2015 General Assembly (Vienna, 12 – 17 April), you can take part in our annual photo competition! From 1 February up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

The ethics of mining

This guest blog post is brought to you by Nick Arndt, Professor at ISTerre and convenor of the the Great Debate at last year’s General Assembly, Metals in our backyard: to mine or not to mine. During the Great Debate the issue of whether the environment impact of mining outweighs the benefits vs. domestic metal production was questioned. With Europe currently importing between 60-100% of the metals that are essential for modern society, this posts explores how realistic it is to advocate for no mining in our own backyards.

Two years ago, in response to massive demonstrations on the streets of Bucharest, the Romania government reversed its decision to allow mining of the Rosia Montana gold deposit. Fierce discussion currently surrounds the Pebble deposit in Alaska, the fifth largest unmined copper deposit. Last summer, protesters derailed mineral exploration in the Rouez region, the first exploration authorized in France for 20 years. In all cases, the activists argued that the environmental risks were so great that mining was unacceptable. The slogan of the French protesters was:

“no mines!!! neither in Rouez, nor anywhere”.

When the Rouez activists were asked where the metals needed for modern society should come from, many answered that improved recycling and substitution would provide the solution. If only this were true! Recycling will indeed provide an increasing proportion of our metals in the future, but for decades to come, new supplies of metals and other mineral products will be required. The vast infrastructure of wind turbines and solar panels needed for a low-carbon society will consume huge amounts of mineral products, not only the well-publicized rare earths and other critical elements, but also enormous quantities of steel, aluminium, concrete and sand. All these materials will be locked up for the 20-30 year lifetime of the structures and will not be available for recycling.

Anti-mining march Auckland New Zealand. Credit: Greg Presland (distributed via Wikimedia Commons)

Anti-mining march Auckland New Zealand. Credit: Greg Presland (distributed via Wikimedia Commons)

To organize their demonstrations, the Rouez and Bucharest activists used cell phones containing numerous rare metals, including cobalt-tantalum that probably came from war-torn central Africa. Some of the titanium might have come from a mine in Norway, and some copper from Poland, but the other metals were imported from outside Europe

The main reason why oil prices have plunged in the past three months is the recent availability of large sources of gas and oil from shale in the USA. While the low prices will have a negative medium-term impact on movements to wean society from fossil fuels, in the short term they may provide a sorely needed boost to struggling European economies. France is in a peculiar position – it has been at the forefront of the movement to ban fracking and has prohibited even the exploration for non-conventional hydrocarbons on its territories, but its feeble economy will benefit from the low energy costs brought about by the availability of American shale-derived oil and gas.

Other Rouez activists recognized that new sources of metals were necessary, but they were adamant that the mining should be done in a manner that caused minimal environmental damage … and preferably far, far away from where they lived. While some metals can be imported to Europe from countries with stable and competent governments like Canada and Australia, most come from Africa, Asia and South America where governments are commonly too weak, too corrupt, or too poor to ensure that mining is done properly. The concerned citizens of Europe and other rich countries prefer that people in other regions put up with the nuisance associated with mining, and if this means that mining is done in places where the operation cannot be done properly, so be it.

The locavore movement argues that we should consume only what is produced within a short distance from where we live. The principle is normally applied to food, and is based on sound principles. Local consumption provides employment to local people and reduces ‘food miles’ – the distance from producers to consumers. But aren’t these ideas equally valid for metals? Is it reasonable and logical to shun green beans from Kenya while consuming copper from the Congo? The Aitik mine illustrates that metals can be produced correctly and efficiently in Europe. This mine, which is located in the far north of Sweden and respects stringent Swedish social and environmental norms, efficiently exploits ore containing only 0.27% Cu, far below the global average.

Rather than adopting the dubious stance that others should bear the burden of supplying the metals needed for European society, is it not more principled to argue that mining should done correctly, and in our own backyard?

By Nick Arndt, Professor at ISTerre & current GMPV Division President

 

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