GeoLog

Geomorphology

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: A solitary floating island

With 2014 officially named the hottest year on record, there is evidence of the effects of rising global temperatures across the globe. The solitary, shimmering iceberg in today’s Imaggeo on Mondays photograph is a reminder that one of the best places to look for evidence of change is in glaciers. Daniela Domeisen tells the story of this lonely frozen block of ancient ice.

Iceberg on Tasman glacier lake. Credit: Daniela Domeisen (distributed via imaggeo.egu.eu)

Iceberg on Tasman glacier lake. Credit: Daniela Domeisen (distributed via imaggeo.egu.eu)

The picture shows an iceberg on Tasman glacier lake in the Southern Alps of New Zealand, in the centre of Aoraki / Mount Cook National Park. The lake consists of melt water from the Tasman glacier, which calves into the lake at its far end. The glacier is one of the largest in New Zealand and flows along New Zealand’s highest peaks, Mt Tasman and Mt Cook.

As most glaciers on Earth, the glaciers in Aoraki / Mount Cook National Park are retreating at a fast pace. The lower parts of the Tasman glacier are at less than 1000m above sea level and are therefore melting especially fast. The Tasman glacier lake has formed over the past two to three decades and has in the meantime reached a length of several kilometers. It is projected to almost double in size as the glacier retreats further.

Icebergs constantly calve from the Tasman glacier into the lake and drift down the lake, driven by a weak current towards the lake’s outflow while melting in the process. The ice contained in the icebergs is several thousand years old, beautifully transparent and clean when looking at a single piece of it.

The pictured iceberg was about 10 meters wide. From its shape, and melting pattern, it is likely that it had turned to its side after calving into the lake. With some force it was possible to tip the smaller icebergs and see a shiny blue surface which had been beautifully polished by the water.

On the lake, everything was completely peaceful and quiet, except for the distant sound of a continuous rippling and trickling coming from the moraines on the sides of the lake, as pictured in the background of the photo. Stones and rocks of various sizes slid down and fell into the lake as the ice inside the moraines melted in the bright, sunny and warm January weather.

The changes which are observed in most places as a result of the changing climate are often either too slow to be observed or invisible to the naked eye. The glacier, its lake and icebergs, however, are continuously changing, and a couple of hours spent on the water give a lively impression of a quiet place where things are changing fast enough to be able to observe a notable difference between the time one enters and leaves the place. The beauty of the glacier and its lake with the glittering icebergs provide a spectacular glimpse of a transient place.

By Daniela Domeisen, Research Analyst, MarexSpectron, London

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.

Imaggeo on Mondays: Artists’ Paint Pots

Many artists draw inspiration from nature and it’s not surprising when faced with landscapes which are as beautiful as the one featured in this week’s Imaggeo on Mondays post. Josep Miquel Ubalde Bauló writes about the origin of the colourful mud pots and bobby-socks trees!

Artists' Paintpots in Yellowstone National Park Credit: Josep Miquel Ubalde Bauló (distributed via imaggeo.egu.eu)

Artists’ Paintpots in Yellowstone National Park. Credit: Josep Miquel Ubalde Bauló (distributed via imaggeo.egu.eu)

This picture corresponds to The Artist Paint Pots, found in in Yellowstone, the first National Park of the world. Yellowstone is one of the most geologically dynamic areas on Earth. A huge underlying magma body releases enormous amounts of heat , which feed more than 10000 hydrothermal features (geysers, hot springs, mudpots, fumaroles), approximately half of all those found in the world.

The Artist Paint Pots is a small geothermal area, which was named after the pastel multicoloured mud pots. Much of the water in these mud pots is near boiling (85 ºC), meaning it is is difficult for life to thrive in them . Only some cyanobacteria and algae can live under these extreme conditions, and they are responsible for the beautiful colours in the mud pots.

The mud pots are acidic thermal features with a limited water supply. For their formation they require sulphite-reducing bacteria, which use hydrogen sulphide for energy, giving sulphuric acid as a waste product. The acidic water slowly dissolves the surrounding rocks, forming fine particles of silica and clay. This viscous clay-water mixture creates a muddy area, with the hot mud boiling and gas bubbling at the surface. The paint pots are coloured mud pots, which range from pink to bright red to purple, due to the iron oxides, potassium, and magnesium in the soil. The reason for the colours in the mud pots is a lack of sulphur. When sulphur is present, it reacts with iron oxides forming pyrite, which is grey.

In this area you can observe some groups of standing-dead trees. Whilst some of them burned in the fires of 1988 (during an unusually dry summer), others have been killed by the runoff from nearby thermal features, which flooded the area around the trees. Minerals in the water plugged the base of the trees and killed them, leaving their bases white. Those trees are known as bobby-socks trees.

By Josep Miquel Ubalde Bauló, Soil Scientist, Miguel Torres Winery

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/.

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