GeoLog

natural hazard

Imaggeo on Mondays: A dramatic avalanche from Annapurna South

Imaggeo on Mondays: A dramatic avalanche from Annapurna South

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 South (pictured in today’s featured image), the 101st tallest peak in the world, towers 7219 m above sea level.

Glaciers in High Mountain Asia, a region that includes the Himalayas, contain the largest volume of ice outside the polar regions. The water trapped, as ice, in the glaciers of the Himalayas is an important source of drinking water, water for irrigation and water for hydropower generation throughout the region. As the Earth’s climate changes and negatively affects glaciers world-wide, scientists are working hard to understand what increased glacier melting means for the communities which depend on them.

Emily Hill is one such scientist. Her and a team of colleagues spent 2 weeks at Annapurna Base Camp in Nepal conducting measurements on the debris covered South Annapurna Glacier.

“We frequently heard avalanches but often they were over too quick to capture on camera. Fortunately, this was one of the largest and the camera was at the ready. These avalanches are an important source of mass for the glacier below,” reminisces Emily.

Glaciers accumulate ice throughout the winter months, as snow adds to the glacial column during the cold months. In addition, avalanches deliver additional snow throughout the year.

“I’m not too sure of the scale of the avalanche, it could probably have been a couple of 100 m across. The avalanche occurred early afternoon when the solar radiation was highest and increased melt is likely to have caused the failure,” describes Emily.

Avalanches in the region are not only an important source of mass accumulation for many of the glaciers, they also pose a hazard not only to climbers of these mountains but also further down along the tourist trail up to Annapurna Base Camp, where there is an avalanche risk section of the route.

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: Sedimentary record of catastrophic floods in the Atacama desert

Imaggeo on Mondays: Sedimentary record of catastrophic floods in the Atacama desert

Despite being one of the driest regions on Earth, the Atacama desert is no stranger to catastrophic flood events. Today’s post highlights how the sands, clays and muds left behind once the flood waters recede can hold the key to understanding this natural hazard.

During the severe rains that occurred between May 12 and 13, 2017 in the Atacama Region (Northern Chile) the usually dry Copiapó River experienced a fast increase in its runoff. It caused the historic center of the city of Copiapó to flood and resulted in thousands of affected buildings including the University of Atacama.

The city of Copiapó (~160,000 inhabitants) is the administrative capital of this Chilean Region and is built on the Copiapó River alluvial plain. As a result, and despite being located in one of the driest deserts of the world, it has been flooded several times during the 19th and 20th century. Floods back in 2015 were among the worst recorded.

The effects of the most recent events are, luckily, significantly milder than those of 2015 as no casualties occurred. However, more than 2,000 houses are affected and hundreds have been completely lost.

During this last event, the water height reached 75 cm over the river margins. Nearby streets where filled with torrents of mud- and sand-laden waters, with plant debris caught up in the mix too. Once the waters receded, a thick bed of randomly assorted grains of sand  was deposited over the river banks and urbanized areas.

Frozen in the body of the bed, the sand grains developed different forms and structures. A layer of only the finest grained sediments, silts and clays, bears the hallmark of the final stages of the flooding. As water speeds decrease, the finest particles are able to drop out of the water and settle over the coarser particles. Finally, a water saturated layer of mud, only a few centimeters thick, blanketed the sands, preserving the sand structures in 3D.

The presence of these unusual and enigmatic muddy bedforms has been scarcely described in the scientific literature. A new study and detailed analysis of the structures will help better understand the sedimentary record of catastrophic flooding and the occurrence of high-energy out-of-channel deposits in the geological record.

By Manuel Abad and Tatiana Izquierdo, Universidad de Atacama (Chile)

 

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: Lusi from the sky with drones

Lusi from the sky with drones. Credit: Giovanni Romeo, Adriano Mazzini and Giuseppe Di Stefano. (distributed via imaggeo.egu.eu)

Lusi from the sky with drones. Credit: Giovanni Romeo, Adriano Mazzini and Giuseppe Di Stefano. (distributed via imaggeo.egu.eu)

The picture shows a spectacular aerial view of a sunset over the Lusi mud eruption in East Java, Indonesia. Here thousands of cubic meters of mud, are spewed out every day from a 100 m sized central crater. Since the initial eruption of the volcano in 2006, following a 6.3 M earthquake, a surface of about 7 km2 has been covered by boiling mud, which has buried more than 12 villages and resulted in the displacement of 40,000 people.

Monitoring Lusi is part of multidisciplinary project called Lusi Lab, which focuses on the study of the behaviour of this incredible mud eruption. Many unsolved questions remain: What lies beneath Lusi? Research focuses on trying to ascertain what triggers the mud eruptions. One key question is whether Lusi is truly a mud volcano, or is it connected to a hydrothermal system linked to the nearby Arjuno Welirang volcanic complex? Lusi erupts mud, water, gas and clasts in pulses and scientists do not fully understand how the intermittent activity is linked to the seismic activity of the neighbouring volcanic complex. For the purposes of hazard and risk management, much speculation has focused on how long is the activity at Lusi is likely to last.

In an attempt to shed light on some of these questions the Lusi Lab team continually collect water and gas samples from the volcano, as well as assessing the seismic activity in the region ( including the neighbouring volcanic arc) through the deployment of a network of seismometers. This data gathering effort is further supported by a UAV prototype: The Lusi drone (assembled and equipped by INGV, Rome). The drone is able to access extreme environments and can provide photogrammetric and thermal images, gas and mud sampling and contact temperature measurements. A permanently installed Gopro Hero3 camera provides a continuous recording over the mud flows during flights, including this week’s Imaggeo on Mondays image.  Gas and water samples collected from the crater site revealed that Lusi is part of a Sedimentary Hosted Geothermal System (SHGT) that connects Lusi with the neighbouring Arjuno Welirang volcanic complex that can be seen in the background of the picture. The eruption site is continuously fed by new surges of geothermal fluids released from the volcano in particular after frequent seismic events occurring in the subduction zone in southern Java.

By Laura Roberts Artal and Giovanni Romeo 

To learn more about Lusi take a look at this paper:

Mazzini, A., Etiope, G., and Svensen, H. (2012), A new hydrothermal scenario for the 2006 Lusi eruption, Indonesia. Insights from gas geochemistry: Earth and Planetary Science Letters, 317-318. 0, 305-318.

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/.