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Imaggeo on Mondays: Earthquake Lake

Imaggeo on Mondays: Earthquake Lake

Despite its alluring turquoise waters and rugged mountain backdrop the story behind this beautiful lake is rather more troubling. In today’s Imaggeo on Mondays, the first post since our short break from the traditional format during the General Assembly, Alexander Osadchiev writes about the shaky origins of Sarez Lake.

Lake Sarez is situated in Tajikistan, deep in the Pamir Mountains. In 1911 a local earthquake caused a large landslide which blocked the valley of the relatively small Murgab River (which discharge is only 100-150 m^3/s). The valley is relatively young, on the geological scale at least, meaning it is deep and narrow and has steep sided slopes. This is the reason why the moderate volume of the landslide (about 2 km^3) was enough to form the tremendously high Usoi dam (about 550 m) – the tallest in the world either natural or man-made. The length of the Usoi dam is about 500 m which is almost equal to its height. However, lakes formed by landslide dams blocking river valleys are not uncommon in the Pamir Mountains or elsewhere around the world.

Most blocking dams are not high or solid enough to remain in place for extended periods of time. Initially, a river will seep through the dam eroding it, but usually the outflow discharge is less than the river inflow into the lake. Together with active sedimentation and silting, the water level in the lake steadily increases until it reaches the dam height. Eventually water starts flowing over the top of the dam and intensively destroys the dam. Yet due to a number of circumstances the behavior of the Sarez Lake was significantly different. On the one hand, the Usoi dam is solid enough not to have been significantly eroded in the more than one hundred years since it appeared. At the same time, it is porous: outflow and inflow volumes of water across the dam balance each other.  Crucially, this balance was obtained for a very high water level, close to the height of Usoi dam itself. Lake water levels oscillate near 500 m height, just 50m away from the top of the of 550 m dam. The height of the dam resulted in the large size of the Sarez Lake – its length is about 60 km and its volume exceeds 16 km^3.

This large volume of water (and potential energy!) situated high in the mountains (3263 m above the sea level) presents a hazard for millions of people in Tajikistan, Afghanistan, and Uzbekistan living below the Sarez Lake and along the banks of the Mugrab, Panj and Amu Darya rivers. The Usoi dam is solid enough to resist erosion and create such a big lake, but it is not known if it can withstand a big earthquake, which are not uncommon in the area. Not only can an earthquake directly destabilize Usoi dam, but an earthquake-induced landslide into the lake could cause a lake tsunami and result in the dam overflowing. Particularly, an area of friable soil forming a unstable slope, has been particularly identified as a risk. Following a large earthquake (8-9 on the Richter scale) it could presumably form a landslide.

The levels of monitoring and investigation of landslide hazards in the region and the risk presented by Lake Sarez itself are still largely understudied. Limited funding availability in Tajikistan and the remoteness of the lake – it can only be reached on foot, after several days of strenuous mountain trekking through an almost uninhabited, but unbelievably beautiful area – are amongst the main reasons this is so.

“The view of the Sarez Lake was the best prize for me and Zhamal Toktamysova at the final part of our 2-week trekking through the Pamir Mountains”, explains Alexander.

 

By Alexander Osadchiev, Shirshov Institute of Oceanology, Physical Oceanography, Moscow

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 Sciences 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.

Sending GIFT to Africa: A new collaboration between the EGU, UNESCO and ESA

For the past ten years, the EGU’s Geosciences Information for Teachers (GIFT) workshops – spreading first hand scientific research to teachers of primary and secondary schools – have been hugely successful in shortening the time that research takes to disseminate from scientist to textbook to teacher and offering usable practical activities for the classroom. GIFT workshops are usually held at the EGU General Assembly in Vienna, adding to the experience of the teachers by immersing them in a world of geoscientific research and discussion. In recent years, workshops have also been held in association with Alexander von Humboldt conferences in Mexico, Malaysia and Peru and are now on the way to Africa.

UNESCO’s Earth Science Education Initiative in Africa was set up to support the development of the next generation of African Earth scientists. The initiative aims to provide the necessary tools, networks and perspectives to apply sound science to solving the challenges of sustainable development and in turn gathering opportunities from them. Challenges and opportunities range from evolution in mineral extraction techniques to environmental management including mitigation of climate change, prevention of natural hazards, and ensuring access to clean drinking water.

Education is key to forging the next generation of ‘Earth stewards’ and give Earth sciences a status that reflects the importance that this discipline plays in the everyday life of African people. One of the three initial activities of the initiative was a focus on Earth science education at primary and secondary level in schools. To achieve this, it was recognised that first providing teachers with the necessary information, conveyed in an engaging way by scientists was essential for inspiring and educating future generations.

Bringing together the expertise of the EGU with UNESCO’s Earth Science Education Initiative in Africa, the EGU are proud to announce a new series of annual GIFT workshops to be held around the African continent over the next four years. As international events, the workshops will be held in four different regions of Africa, starting with Southern Africa. They will cover various topics of societal relevance such as climate change, groundwater, geohazards, mineral resources and environmental sustainability. The UNESCO-EGU-ESA African GIFT workshops will take place over the course of 3 days with 40 teachers from across the region and 8-10 speakers, half of whom will be non-African experts. Secondary-school science teachers can apply to participate in the South African GIFT workshop by filling in an online form or sending their application materials to sa-loc@egu.eu by January 24. The application information is available for download in PDF format, a document which also includes further details about the UNESCO-EGU-ESA GIFT workshops.

Partners

At the EGU, the Committee on Education will be responsible for developing the programme with the help of the new EGU Educational Fellow. Programme specialists from the Division of Ecological and Earth Sciences at UNESCO headquarters, Paris and UNESCO African field offices will be jointly organising the workshops. For the first UNESCO-EGU-ESA GIFT workshop, to be held from the 26th-28th February 2014 in Port Elizabeth, South Africa, the European Space Agency and African Earth Observatory Network will be offering support and expertise and the Nelson Mandela Metropolitan University will be hosting the workshop. To reflect on one of the most pressing societal issues and the release of the 5th Assessment Report of the IPCC, the first workshop will be on ‘Climate Change and Human Adaptation’.

With preparations already underway for this first African workshop, all those involved are looking forward to a successful event that will become a sustainable part of teacher education in Africa.

By Carlo Laj (Chair of the EGU Committee on Education), Sarah Gaines (Assistant Program Specialist, UNESCO) and Jane Robb (EGU Educational Fellow)

Update (11/12/13): The closing date for applications has been extended to 24 January 2014.