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Imaggeo on Mondays: Annapurna snow avalanche

Imaggeo on Mondays: Annapurna snow avalanche

The Annapurna massif is located in an imposing 55 km long collection of peaks in the Himalayas, which behave as a single structural block. Composed of one peak (Annapurna I Main) in excess of 8000 m, a further thirteen peaks over 7000 m and sixteen more of over 6000 m, the massif forms a striking structure within the Himalayas.

Annapurna I Main, the tenth highest peak in the world, is towering at an impressive 8,091 m. Renowned for its difficult climbing conditions, it holds one of the highest fatality rates of the 8000+ peaks. October 2014 marked a particular dark period in the mountain’s climbing history when 39 trekkers were killed during severe snowstorms and avalanches while completing a popular hike circling Annapurna I.

Martin Struck, a PhD student at the University of Wollongong, Australia, captured this extraordinary photograph of a surging avalanche early one morning in October 2012. Martin visited the Annapurna massif as part of his Diploma project at the University of Potsdam about suspended sediment fluxes in the Kali Gandaki River which cuts the world’s deepest gorge through the Himalayas between the Annapurna and Dhaulagiri massifs. The snow avalanche careered down the ~35° sloping northeast flank of Tilicho himal, a peak only 10 km away from the Annapurna I summit.

“The avalanche is one of five I spotted that morning in the area. The tracks and runout zones of previous snow and/or dry snow avalanches are clearly visible in the image,” describes Martin.

He explains that rising morning temperatures triggered the avalanches, causing the failure of stable snow which had fallen on the night before.

The area is close to Tilicho Lake, located at about 4900 m above sea level, and one of many Himalayan glacial lakes which play a crucial role in the supply of water to the inhabitants of Nepal.

“Snow and glacial melt contribute approximately 10% to the annual discharge of the main Nepalese rivers, but are of significant important outside the monsoon season,” explains Martin.

Earlier on this year, a study published in the open access journal, The Cryosphere, found that if greenhouse-gas emissions continue to rise, glaciers in the Everest region of the Himalayas could experience dramatic change in the decades to come. The glacier model used in the paper shows that glacier volume could be reduced between 70% and 99% by 2100. The findings have important implications for the future availability of water in the region: a significant decrease in glacial volume would have consequences for agriculture and hydropower generation. You can learn more about this research and it’s consequences in this Press Release: Glacier changes at the top of the world – Over 70% of glacier volume in Everest region could be lost by 2100.

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/.

Geosciences Column: Earthquakes and depleted gas reservoirs; what comes first?

Geosciences Column: Earthquakes and depleted gas reservoirs; what comes first?

An ever growing population means the requirement for resources to fuel our modern lifestyles grows too. Be it in mining, oil/gas extraction or the improvement of renewable technologies, the boundaries of where and how we access resources are constantly being pushed. Previously inaccessible resources become viable prospects as demand increases and our technological know-how advances.

Hand in hand with technological advances, comes an increased awareness of the environment and how it may be affected by the new practices. While the need for more energy is clear, more and more, energy consumers want to understand the impacts of sourcing the energy in the first place. For instance, how seismicity is linked to the extraction of natural resources, namely gas and oil, has become an area of intense research, as well as of media, political and societal focus.

Fracking – the process by which a high pressure mixture of water, sand and chemicals is injected into reservoirs of low porosity and permeability to encourage natural gas trapped within the rock to flow to the surface – makes regular headlines. The debate as to what extent hydraulic fracturing (the formal name for fracking) of rocks, and the subsequent disposal wastewater generated as a by-product, might induce earthquakes is ongoing.

Now, let’s flip the problem, to one which is little studied and even less well understood. What are the risk associated with exploiting conventional oil and gas reservoirs in areas which are earthquake prone? This is exactly the question asked in a recently published paper by Mucciarellie, Dona and Valensise, in the open access journal, Natural Hazards and Earth System Science.

A case study: The Po Plain

In order to explore the problem, the researchers focused on the Po Plain, an alluvial plain which extends for some 45 000 km² (an area roughly half the size of Portugal), over northern Italy. It sits at the foothills of the southern Alps and is bound by the Northern Apennines to the south.

Simplified sketch of northern Italy, centred on the Po Plain and showing the southern Alps and Northern Apennines fold and thrust belts. The location of the largest shocks of the May 2012 Emilia earthquake sequence is shown with red stars. The yellow rectangle outlines the study area (see Fig. 2). Key: SAMF: southern Alps mountain front; SAOA: southern Alps outer arc; GS: Giudicarie system; SVL: Schio-Vicenza line; NAOA: Northern Apennines outer arcs; PTF: pede-Apennines thrust front; MA: Monferrato arc; EA: Emilia arc; FRA: Ferrara-Romagna arc. Modified from Vannoli et al. (2015). Taken from Mucciarelli et al. (2015).

Simplified sketch of northern Italy, centred on the Po Plain and showing the southern Alps and Northern Apennines fold and thrust belts. The location of the largest shocks of the May 2012 Emilia earthquake sequence is shown with red stars. The yellow rectangle outlines the study area Key: SAMF: southern Alps mountain front; SAOA: southern Alps outer arc; GS: Giudicarier system; SVL: Schio-Vicenza line; NAOA: Northern Apennines outer arcs; PTF: pede-Apennines thrust front; MA: Monferrato arc; EA: Emilia arc; FRA: Ferrara-Romagna arc. Modified from Vannoli et al. (2015). Taken from Mucciarelli et al. (2015). Click to enlarge.

Since the 1950s the Po Plain has been systematically exploited for gas and oil. Its structural make-up is similar to many other oil and gas fields world-wide: the reservoir is hosted by growing anticlines (a type of fold which forms an ‘A’ shape) which extend to depths which are seismogenically active. It makes for an ideal case study.

The plain obscures two fold and thrusts belts, – areas of deformed sedimentary rock in which the layers are folded and duplicated by thrust faults – formed due to the proximity to the large orogens. The belts are still contracting, as the European and Adriatic plates continue to collide into one another. The contraction is accommodated by a number of faults in the area which have the potential to generate M 5.5+ earthquakes.

Indeed, the Po Plain was hit by a series of earthquakes and aftershocks in May and June 2012 which ranged in magnitude between 5.9 and 5.1. The costs of the earthquakes were significant, with as many as 100 buildings of historical importance being damaged or destroyed and the tragic loss of 25 lives.

Soon after the earthquakes, speculation start to mount as to whether they might be related to the hydrocarbon exploitation in the area; a notion which came as a surprise to scientists and oil industry professionals alike given that, at the time, studies of induced seismicity in Italy were rare.

Links between hydrocarbon fields and seismicity

Mucciarelli (author of the study) and his co-workers focused on an approximately 150km by 70km section of the Po Plain. They identified a total of 455 drilled wells in the area for the purposes of extraction of hydrocarbons: 190 of which were found to be productive (wells that have been or are producing oil/gas), while 227 were sterile and haven’t been exploited. The geology of the units in the area is generally homogenous and cannot account for the difference in productivity. So, what is the cause?

In a (somewhat simplified) conventional system, oil and gas typically forms in carbon rich shales which act as the source rocks. The hydrocarbons then migrate and accumulate in reservoirs, which are usually formed of permeable and porous rocks such as sandstones. These are capped by a sealing unit of shale or chalk (amongst others), which prevents the hydrocarbons accumulated in porous layers from escaping.

For a reservoir to be productive, the cap rock must be intact and unaffected by fractures or faults which might allow the fluids to escape – something which is not guaranteed in an area prone to earthquakes as is the Po Plain.

Mucciarelli et al. highlight that earthquakes of M 5.5 and above have the potential to cause movement on existing faults leading to new fractures, as well slip on existing faults, thus damaging cap rocks and rendering some reservoirs in the region unproductive as the hydrocarbons would be free to escape. Their argument is strengthened by the finding that a number of the sterile wells they identified cluster around the faults which caused the 2012 earthquakes, while productive wells are found a few kilometres distance away.

What the findings mean for prospective oil and gas fields

Through detailed statistical analysis, the researchers were able to define the characteristics of the productive and sterile areas in greater detail. They found that broader anticlines were less likely to be structurally sound as they were formed by wider, deeper and longer faults which in turn, could be the source of earthquakes. A cluster of unproductive wells would identify such regions during prospecting stages. Conversely, areas of productive wells identify areas unable to generate large earthquakes which would threaten the integrity of the reservoirs. Typically, these would also coincide with smaller anticlines.

The results have implications, not only for the oil and gas industry, but also for underground storage facilities. A CH4 storage facility was being built in an oil depleted reservoir right above the source of one of the May 2012 earthquakes. The research presented in the paper, combined with results from an earlier study by Evans in 2008, show that preference should be given to depleted gas reservoirs over depleted oil and aquifer reservoirs, when designing a gas storage facility in tectonically active areas.

The authors acknowledge that the Po Plain was an ideal case study in which to test their hypothesis. Study of other hydrocarbon producing regions, such as California, North Africa and the Middle East, is now required to fully validate the findings.

References

Evans, D.J.: An appraisal of underground gas storage technologies and incidents, for the development of risk assessment methodology, Prepared by the British Geological Survey for the Health and Safety Executive 2008, RR605 Research Report, 264 ++ tables, figures and appendix, available at: http://www.hse.gov.uk/research/rrpdf/rr605.pdf, 2008.

Mucciarelli, M., Donda, F., and Valensise, G.: Earthquakes and depleted gas reservoirs: which comes first?, Nat. Hazards Earth Syst. Sci., 15, 2201-2208, doi:10.5194/nhess-15-2201-2015, 2015.

Vannoli. P., Burrato, P., and Valensise, G.: The Seismotectonics of the Po Plain (Northern Italy): Tectonic Diversity in a Blind Faulting Domain, Pure Appl. Geophys., 172, 1105-1142, doi:10.1007/s00024-014-0873-0, 2015.

Imaggeo on Mondays: Drilling a landslide

Imaggeo on Mondays: Drilling a landslide

That landslides are hazardous goes without saying; the risk posed by them will largely depend on where they occur and their exact characteristics, which makes understanding the mechanisms which trigger them, as well as predicting when they might happen, extremely difficult. Today’s Imaggeo on Mondays image, brought to you by Ekrem Canli, a PhD student at the University of Vienna, is an example of how scientists are trying to get a better handle on landslide mechanics.

The Salcher landslide is situated in the transition zone between the Flyschzone and the Klippen Zone; both belonging to the most landslide prone areas in Austria exhibiting almost 5 landslides per km². Flysch materials in that area consist of alternations of fine grained layers (clayey shales, silty shales, marls) and sandstones, whereas the Klippen Zone is covered by a sequence of marly beds with intercalated sandy limestones.

Our featured Imaggeo picture shows students during field work at the Salcher landslide observatory in Gresten (Austria) extracting sediment cores from percussion drilling – a technique in which core samplers are driven into the soil by repeated hammer blows using a percussive drilling rig.

The Salcher landslide observatory was initiated in 2014 as a long term monitoring project (10+ years). On the one hand, an increased frequency of landslide occurrences in many parts of the world is commonly listed as an expected impact of human-induced climate change. On the other hand, the lack of historic or long term monitoring information on landsliding makes is difficult to correlate landslide occurrence and its triggering event (e.g. intense rainfall, ground vibrations) with past and potentially future conditions. Additionally, most landslides are not in a constantly active state – meaning they are at rest and not moving downslope – but are only reactivated after certain triggering events before they eventually come to a halt again. This dormant state may cover several years or even longer, which most landslide monitoring efforts do not cover so far. Consequently, monitoring systems with automated instrumentation, which allows for regular, remote observations to be gathered, have been of great value in the past in terms of understanding forthcoming landslide dynamics.

The monitoring setup at the Salcher landslide observatory covers current state-of-the-art methods in landslide investigation (such as inclinometers, piezometers, TDR probes, etc., see this paper for more information on monitoring landslides) combined with rather new and innovative techniques, such as permanent terrestrial laser scanning (pTLS – for an automated high resolution surface change detection on a daily basis) or permanent ERT (Electrical resistivity tomography) for spatially monitoring the propagation of rainwater in the subsurface every three hours. Additionally, percussion drillings and dynamic probing was performed on a longitudinal section of the landslide for a better structural interpretation of the landslide subsurface.

And on a more personal side note: everything looks so shiny and bright while presenting results on conferences…most of the time, however, you spend time on fixing (and cursing) things in the field that seem not to work for any particular reason. You are not alone out there!

By Ekrem Canli, PhD student, University of Vienna (ENGAGE working group on Geomorphological Systems and Risk Research).

 

References

Canli, E., Thiebes, B., Engels, A., Glade, T., Schweigl, J., and Bertagnoli, M.: Multi-parameter monitoring of a slow moving landslide in Gresten (Austria), Geophysical Research Abstracts, Vol. 17, EGU2015-223-3, EGU General Assembly 2015

Canli, E., Höfle, B., Hämmerle, M., Thiebes, B., and Glade, T.: Permanent 3D laser scanning system for an active landslide in Gresten (Austria), Geophysical Research Abstracts, Vol. 17, EGU2015-2885-2, EGU General Assembly 2015

Crozier,M.J.: Deciphering the effect of climate change on landslide activity: A review, Geomorphology, Volume 124, Issues 3–4, doi:10.1016/j.geomorph.2010.04.009, 2010

Petschko, H., Brenning, A., Bell, R., Goetz, J., and Glade, T.: Assessing the quality of landslide susceptibility maps – case study Lower Austria, Nat. Hazards Earth Syst. Sci., 14, 95-118, doi:10.5194/nhess-14-95-2014, 2014.

Supper, R., Ottowitz, D., Jochum, B., Kim, J.-H., Römer, I., Pfeiler, S., Lovisolo, M., Gruber, S., and Vecchiotti, F.: Geoelectrical monitoring: an innovative method to supplement landslide surveillance and early warning, Near Surface Geophysics, Volume 12, Issue 1, doi:10.3997/1873-0604.2013060, 2014

Wieczorek, G.F., and Snyder, J.B.: Monitoring slope movements, in Young, R., and Norby, L., Geological Monitoring: Boulder, Colorado, Geological Society of America, p. 245–271, doi: 10.1130/2009.monitoring, 2009,

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/.

 

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