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Natural Hazards

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/.

Imaggeo on Mondays: Landslide on the Cantabrian coastline

Shimmering blue seas, rocky outcrops and lush green hills sides; this idyllic landscape is punctuated by a stark reminder that geohazards are all around us. Irene Pérez Cáceres, a PhD student at the University of Granada (Spain) explains the geomorphology behind this small scale landslide on the Asturian coastline.

Landslide on the Cantabrian Sea. Credit: Irene Pérez Cáceres (distributed via imaggeo.egu.eu)

Landslide on the Cantabrian Sea. Credit: Irene Pérez Cáceres (distributed via imaggeo.egu.eu)

This picture was taken in May 2011 in the coast of Llanes (Asturias, Spain). I was living in Oviedo (Asturias, Spain) doing my Master in the structural geology of the Axial Zone of the Pyrenees. Thus, geomorphology and geohazards are not my specialty or area of expertise. However, the landslides are well known and studied in this region, and people from Asturias call them Argayos.

This argayo is situated in Niembru Mountain, over the San Antolín beach, constantly affected by waves and swell of tides of the Cantabrian Sea, and continuous rain typical in the region. It was defined as a rotational landslide with two fracture surfaces, possibly conjugated in wedge shape. It is approximately 50 meters high and 60 meters width at its base. The slide volume is calculated at 45000 m3. It is carved in quartzite altered by the water rain infiltration through crevices in the surface. The initial displacement was between 10 and 15 meters in the scar. Experts say this landslide is still active, moving and evolving continuously. It is an imminent risk for the swimmers, but it is very difficult to control it, due to the size and the slope, and the technical requirements to stabilize the rock. On the other side of this mountain, further landslides are evident, as a result of the building of a road.

These natural geomorphological processes are very common in the north of Spain, mainly in riverbeds, as well in other nearby beaches. The main causes are the abundant (and sometimes heavy) rainfall, the typically clay rich soils, steep slopes, building works that destabilize the slopes, and the absence of vegetation in some areas. They vary in in size and volume, and can sometimes have important material consequences and can pose a significant risk for the local inhabitants. The annual economic cost for repairing the damage caused by these processes is estimated to be 66 million of euros in this region.

Studies carried out in the Department of Geology of the University of Oviedo (Mª José Domínguez and her group), indicate that 70% of the landslides in Asturias happen when it rains over 200 mm during over a period of a minimum of three days. Research has also been carried out to try and predict when landslides might happen, examining numerous landslides over the last 20 years approximately. It seems that one conditioning factor is the exact location of new buildings, being that ancient constructions used to be in secure zones, probably because people observed more minutely to the nature, but the new ones are more vulnerable.

To conclude, detailed geological and geomorphological studies are always recommended to carry out before constructions. Thereby it is possible to minimise this common geohazard in Asturias.

By Irene Pérez Cáceres, PhD Student, Granada University.

 

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/.

Geosciences Column: Do roads mean landslides are more likely?

Geosciences Column: Do roads mean landslides are more likely?

Landslides have been in the news frequently over the past 12 months or so. It’s not surprising considering their devastating consequences and potential impact on nearby communities. Data collected by Dave Petley in his Landslide Blog shows that from January to July 2014 alone, there were 222 landslides that caused loss of life, resulting in 1466 deaths.

A recent paper, in the journal Natural Hazards and Earth System Science investigates, what the potential effects of human denudation can have on the occurrence of landslide events. There is no denying that landslide susceptibility has been increased by human activity. Global warming and greater precipitation are key contributing factors to the rise in the number of landslides which occur globally. On a local scale, the building of infrastructure, particularly roads and felling of trees to make way for agriculture are largely to blame for increased numbers of slides and slumps.

Overview of the study area with mean annual precipitation patterns (top panel), and its location in southern Ecuador (lower left panel). Highways Troncal de la Sierra E35 and Transversal Sur E50 extend in the north–south and east–west direction, respectively. The numbers along the street refer to the corresponding geological unit (1: unconsolidated rocks; 2: sedimentary rocks; 3: volcanic rocks; 4: metamorphic rocks; 5: plutonic rocks). The area of the detailed map (lower right panel) will be used as a sample area for the visualization of a predictive map in Fig. 5. Precipitation data are taken from the study of Rollenbeck and Bendix (2001). From Brenning et al., (2015)

Overview of the study area with mean annual precipitation patterns (top panel), and its location in southern Ecuador (lower left panel). Highways Troncal de la Sierra E35 and Transversal Sur E50 extend in the north–south and east–west direction, respectively. The numbers along the street refer to the corresponding geological unit (1: unconsolidated rocks; 2: sedimentary rocks; 3: volcanic rocks; 4: metamorphic rocks; 5: plutonic rocks). Precipitation data are taken from the study of Rollenbeck and Bendix (2001). From Brenning et al., (2015). Click on the image for a larger version.

The research presented in the paper focuses on landslides along mountain roads in Ecuador, where drainage systems and stabilisation of hillsides is often inadequate and is known to increase the likelihood of landslides. This problem is not exclusive to Ecuador and is often linked to poorer infrastructure and engineering in developing countries. In addition, the study area is a tropical mountain ecosystem, which is naturally more sensitive and prone to landslides. The key question here being: are more landslides likely to happen close to a road (in this particular case an interurban highways), or does greater distance from them offer some hazard relief?

The geology, and local climate and vegetation are important factors to also take into consideration when carrying out an assessment of this nature. Highways E35 and E50 run along Southern Ecuador and intersect the Cordillera Real, which creates a strong local climate divide and generates a precipitation gradient along the area studied. Páramo ecosystems are dominant towards the east, whilst tropical dry forests are common in the west. The geology is also variable across the area studied: dipping and jointed metamorphic rocks are dominant, but are in contact with horizontally layered sedimentary units of loose conglomerates and sandstones. Additionally, the hill sides running along the highways are often deforested to make way for coffee, sugar cane and banana crops. When they are not, they are commonly handed over to cattle for grazing.

By mapping, in great detail, all landslide occurrences within a 300m corridor along the highways, the researchers were able to digitise 2185 landslide initiation points! In total, 843 landslides were mapped and classified by recording the type of movement experienced, as well as the material type (soil, debris or rock) and whether the slide was still active, inactive or had been reactivated. The detailed data meant it was possible to statistically model the likelihood of landslides occurring in close proximity to the highway (25m) vs. some distance away (200m). The results showed that susceptibility to landslides increases by one order of magnitude closer to the highway when compared to areas between 150-300 m away from the mountain road. Furthermore, slides close to the highway were found to be more likely to be reactivated than those a greater distance away.

The study found that the local topography, geology and climate conditions had a lesser influence on the likelihood of landslides. However, the influence of stretches of mountain road constructed in the sedimentary units seems to enhance the hazard.

Landslides occurring along the investigated highways. (a) Typical landslides of the wet metamorphic part of the study area in the east. (b) Typical landslides of the semi-arid, conglomeratic part of the study area in the west. (c) Highway destroyed by landsliding. (d) A highway is cleared from a recent landslide occurrence. From Brenning et al., (2015).

Landslides occurring along the investigated highways. (a) Typical landslides of the wet metamorphic part of the study area in the
east. (b) Typical landslides of the semi-arid, conglomeratic part of the study area in the west. (c) Highway destroyed by landsliding. (d) A
highway is cleared from a recent landslide occurrence. From Brenning et al., (2015).

In future, the model can be used to predict locations where landslides are more likely to occur along the E35 and E50. Recently, engineering works have been carried out along the studied stretch of highways to stabilise the hillsides. The data collected as part of the research presented in the paper will be useful in the future to monitor the efficacy of the improvements. On a larger scale, further studies of this type could be used by local governments when planning new infrastructure and could lead to incorporation of cost-effective mitigation measures in new developments.

 

By Laura Roberts Artal, EGU Communications Officer

Reference:

Brenning, A., Schwinn, M., Ruiz-Páez, A. P., and Muenchow, J.: Landslide susceptibility near highways is increased by 1 order of magnitude in the Andes of southern Ecuador, Loja province, Nat. Hazards Earth Syst. Sci., 15, 45-57, doi:10.5194/nhess-15-45-2015, 2015.

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