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GeoTalk: To understand how ice sheets flow, look at the bedrock below

GeoTalk: To understand how ice sheets flow, look at the bedrock below

Geotalk is a regular feature highlighting early career researchers and their work. In this interview we speak to Mathieu Morlighem, an associate professor of Earth System Science at the University of California, Irvine who uses models to better understand ongoing changes in the Cryosphere. At the General Assembly he was the recipient of a 2018 Arne Richter Award for Outstanding Early Career Scientists.  

Could you start by introducing yourself and telling us a little more about your career path so far?

Mathieu Morlighem (Credit: Mathieu Morlighem)

I am an associate professor at the University of California Irvine (UCI), in the department of Earth System Science. My current research focuses on better understanding and explaining ongoing changes in Greenland and Antarctica using numerical modelling.

I actually started glaciology by accident… I was trained as an engineer, at Ecole Centrale Paris in France, and was interested in aeronautics and space research. I contacted someone at the NASA Jet Propulsion Laboratory (JPL) in the US to do a six-month internship at the end of my master’s degree, thinking that I would be designing spacecrafts. This person was actually a famous glaciologist (Eric Rignot), which I did not know. He explained that I was knocking on the wrong door, but that he was looking for students to build a new generation ice sheet model. I decided to accept this offer and worked on developing a new ice sheet model (ISSM) from scratch.

Even though this was not what I was anticipating as a career path, I truly loved this experience. My initial six-month internship became a PhD, and I then moved to UCI as a project scientist, before getting a faculty position two years later. Looking back, I feel incredibly lucky to have seized that opportunity. I came to the right place, at the right time, surrounded by wonderful people.

This year you received an Arne Richter Award for Outstanding Early Career Scientists for your innovative research in ice-sheet modelling. Could you give us a quick summary of your work in this area?

The Earth’s ice sheets are losing mass at an increasing rate, causing sea levels to rise, and we still don’t know how quickly they could change over the coming centuries. It is a big uncertainty in sea level rise projections and the only way to reduce this uncertainty is to improve ice flow models, which would help policy makers in terms of coastal planning or choosing mitigation strategies.

I am interested in understanding the interactions of ice and climate by combining state-of-the-art numerical modelling with data collected by satellite and airplanes (remote sensing) or directly on-site (in situ).  Modelling ice sheet flow at the scale of Greenland and Antarctica remains scientifically and technically challenging. Important processes are still poorly understood or missing in models so we have a lot to do.

I have been developing the UCI/JPL Ice Sheet System Model, a new generation, open source, high-resolution, higher-order physics ice sheet model with two colleagues at the Jet Propulsion Laboratory over the past 10 years. I am still actively developing ISSM and it is the primary tool of my research.

More specifically, I am working on improving our understanding of ice sheet dynamics and the interactions between the ice and the other components of the Earth system, as well as improving current data assimilation capability to correctly initialize ice sheet models and capture current trends. My work also involves improving our knowledge of the topography of Greenland and Antarctica’s bedrock (through the development of new algorithms and datasets). Knowing the shape of the ground beneath the two ice sheets is key for understanding how an ice sheet’s grounding line (the point where floating ice meets bedrock) changes and how quickly chunks of ice will break from the sheet, also known as calving.

Steensby Glacier flows around a sharp bend in a deep canyon. (Credit: NASA/ Michael Studinger)

At the General Assembly, you presented a new, comprehensive map of Greenland’s bedrock topography beneath its ice and the surrounding ocean’s depths. What is the importance of this kind of information for scientists?

I ended up working on developing this new map because we could not make any reliable simulations with the bedrock maps that were available a few years ago: they were missing key features, such as deep fjords that extend 10s of km under the ice sheet, ridges that stabilize the retreat, underwater sills (that act as sea floor barriers) that may block warm ocean waters at depth from interacting with the ice, etc.

Subglacial bed topography is probably the most important input parameter in an ice sheet model and remains challenging to measure. The bed controls the flow of ice and its discharge into the ocean through a set of narrow valleys occupied by outlet glaciers. I am hoping that the new product that I developed, called BedMachine, will help reduce the uncertainty in numerical models, and help explain current trends.

3D view of the bed topography and ocean bathymetry of the Greenland Ice Sheet from BedMachine v3 (Credit: Peter Fretwell, BAS)

How did you and your colleagues create this map, and how does it compare to previous models?

The key ingredient in this map, is that a lot of it is based on physics instead of a simple “blind” interpolation. Bedrock elevation is measured by airborne radars, which send electromagnetic pulses into the Earth’s immediate sub-surface and collect information on how this energy is reflected back. By analyzing the echo of the electromagnetic wave, we can determine the ice thickness along the radar’s flight lines. Unfortunately, we cannot determine the topography away from these lines and the bed needs to be interpolated between these flight lines in order to provide complete maps.

During my PhD, I developed a new method to infer the bed topography beneath the ice sheets at high resolution based on the conservation of mass and optimization algorithms. Instead of relying solely on bedrock measurements, I combine them with data on ice flow speed that we get from satellite observations, how much snow falls onto the ice sheet and how much melts, as well as how quickly the ice is thinning or thickening. I then use the principle of conservation of mass to map the bed between flight lines. This method is not free of error, of course! But it does capture features that could not be detected with other existing mapping techniques.

3D view of the ocean bathymetry and ice sheet speed (yellow/red) of Greenland’s Northwest coast (Credit: Mathieu Morlighem, UCI)

What are some of the largest discoveries that have been made with this model? 

Looking at the bed topography alone, we found that many fjords beneath the ice, all around Greenland, extend for 10s and 100s of kilometers in some cases and remain below sea level. Scientists had previously thought some years ago that the glaciers would not have to retreat much to reach higher ground, subsequently avoiding additional ice melt from exposure to warmer ocean currents. However, with this new description of the bed under the ice sheet, we see that this is not true. Many glaciers will not detach from the ocean any time soon, and so the ice sheet is more vulnerable to ice melt than we thought.

More recently, a team of geologists in Denmark discovered a meteorite impact crater hidden underneath the ice sheet! I initially thought that it was an artifact of the map, but it is actually a very real feature.

More importantly maybe, this map has been developed by an ice sheet modeller, for ice sheet modellers, in order to improve the reliability of numerical simulations. There are still many places where it has to be improved, but the models are now really starting to look promising: we not only understand the variability in changes in ice dynamics and retreat all around the ice sheet thanks to this map, we are now able to model it! We still have a long way to go, but it is an exciting time to be in this field.

Interview by Olivia Trani, EGU Communications Officer

Imaggeo on Mondays: Digging out a glacier’s story

Imaggeo on Mondays: Digging out a glacier’s story

This photograph shows landforms on Coraholmen Island in Ekmanfjorden, one of the fjords found in the Norwegian archipelago, Svalbard. These geomorphic features were formed by Sefströmbreen, a tidewater glacier, when it surged in the 1880s.

Although all glaciers flow, some glaciers undergo cyclic changes in their flow. This is called surging, and glaciers that surge are called surging glaciers. During their active phase, surging glaciers speed up and advance. At this time, glaciers collect, transport and deposit large volumes of sediment. This active phase is then followed by a so-called quiescent phase, when glaciers slowdown and retreat. Sediment carried within the ice is then exposed. Often surge-type glaciers produce a characteristic set of landforms, like the red ridges featured here in this photograph.

Only a small proportion of the world’s glaciers surge. Svalbard is home to many of these surging glaciers, and the length of the surge cycle varies by region. A quiescent phase of surging glaciers in Svalbard can last between 10 and 100 years. An active phase is commonly between 1 and 10 years. Surging glaciers are enigmatic; we still do not fully understand all the processes that cause these glaciers to switch between active and quiescent phases.

When Sefströmbreen surged, it advanced over the fjord and overrode Coraholmen Island. The glacier deposited up to 0.2 km3 of sediment on the western side of the island. As a result, the island doubled in size. The red ridges in the foreground of the photograph were formed when sediment under the glacier was squeezed up into crevasses, large cracks in the ice. Once the ice melted, these crevasse-squeezed ridges were exposed. They contrast in colour with grey Kolosseum Mountain in the background.

Glaciers are useful indicators of past climate and they are used for climate reconstructions. However, surging glaciers are not suitable for such reconstructions. This is because glacier surging is not directly related to climate. When a surging glacier advances during its active phase, it does not mean that the climate is colder. This also holds true for the past. If a surging glacier was bigger at some point in the past, it is not because the climate at the time was colder. If we didn’t know that the glacier surged, we would make a wrong inference about climate. Therefore it is important to know which glaciers are surging-type glaciers.

To document surging behaviour of glaciers, we can use historical sources, glaciological observations and satellite images. If no such records exist or if we are interested in time period that precedes satellite observations, we rely on landforms to tell us the story. We can study these landforms, their appearance, shape, structure, and what they’re made of to learn about past behaviour of glaciers, their dynamics, and processes that go on underneath a glacier where it meets its bed.

The photograph was taken during a field cruise as part of the University Centre in Svalbard’s Arctic Glaciers and Landscapes course.

By Monika Mendelova, University of Edinburgh (UK)

References

Boulton, G.S. et al. Till and moraine emplacement in a deforming bed surge — an example from a marine environment. QSR 15, 961-987. 1996

Evans, D.J.A., & Rea, B.R. Geomorphology and sedimentology of surging glaciers: a land-systems approach. Ann. Glaciol. 27, 75 – 82. 1999

Dowdeswell, J.A. et al. Mass balance change as a control on the frequency and occurrence of glacier surges in Svalbard, Norwegian High Arctic. Geophys. Res. Lett. 22, 2909-2912. 1995

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: Hints of an eruption

Imaggeo on Mondays: Hints of an eruption

The photograph shows water that accumulated in a depression on the ice surface of Vatnajökull glacier in southeastern Iceland. This 700m wide and 30m deep depression [1], scientifically called an ‘ice cauldron’, is surrounded by circular crevasses on the ice surface and is located on the glacier tongue Dyngjujökull, an outlet glacier of Vatnajökull.

The photo was taken on 4 June 2016, less than 22 months after the Holuhraun eruption, which started on 29 August 2014 in the flood plain north of the Dyngjujökull glacier and this depression. The lava flow field that formed in the eruption was the largest Iceland has seen in 200 years, covering 84km2 [2] equal to the total size of Manhattan .

A number of geologic processes occurred leading up the Holuhraun eruption. For example, preceding the volcanic event, a kilometre-wide area surrounding the Bárðarbunga volcano, the source of the eruption, experienced deformation. Additionally, elevated and migrating seismicity at three to eight km beneath the glacier was observed for nearly two weeks before the eruption [3]. At the same time, seven cauldrons, like the one in this photo, were detected on the ice surface (a second water filled depression is visible in the upper right corner of the photo). They are interpreted as indicators for subglacial eruptions, since these cauldrons usually form when geothermal or volcanic activity induces ice melt at the bottom of a glacier [4].

Fracturing of the Earth’s crust led up to a small subglacial eruption at the base of the ice beneath the photographed depression on 3 September 2014. This fracturing was further suggested as the source of long-lasting ground vibrations (called volcanic tremor) [5].

My colleagues and I studied the signals that preceded and accompanied the Holuhraun eruption using GPS instruments, satellites and seismic ground vibrations recorded by an array of seismometers [2, 5]. The research was conducted through a collaboration between University College Dublin and Dublin Institute for Advanced Studies in Ireland, the Icelandic Meteorological Office and University of Iceland in Iceland, and the GeoForschungsZentrum in Germany.

The FP7-funded FutureVolc project financed the above mentioned research and further research on early-warning of eruptions and other natural hazards such as sub-glacial floods.

By Eva Eibl, researcher at the GeoForschungsZentrum

Thanks go to www.volcanoheli.is who organised this trip.

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/.

May GeoRoundUp: the best of the Earth sciences from around the web

May GeoRoundUp: the best of the Earth sciences from around the web

Drawing inspiration from popular stories on our social media channels, as well as unique and quirky research news, this monthly column aims to bring you the best of the Earth and planetary sciences from around the web.

Major Story

This month the Earth science media has directed its attention towards a pacific island with a particularly volcanic condition. The Kilauea Volcano, an active shield volcano on the southeast corner of the Island of Hawai‘i, erupted on 3 May 2018, following a magnitude 5.0 earthquake that struck the region earlier that day.

Since the eruption, more than two dozen volcanic fissures have emerged, pouring rivers of lava onto the Earth’s surface and spurting fountains of red-hot molten more than 70 metres into the air.  As of today, Kilauea’s eruption has covered about 3534 acres (14.3 square kilometres) of the island in lava, according to the U.S. Geological Survey’s most recent estimates.

The island’s volcanic event has dealt heavy damages to the local community, forcing thousands of locals to evacuate the affected area. On 4 May, the governor of Hawaii, David Ige, declared a local state of emergency, activating military reservists from the National Guard to help with evacuations. Over the month Kilauea’s eruption has engulfed nearby neighborhoods in an oozing layer of lava, overtaking 75 homes, blocking major roads, swallowing up many vehicles, and even briefly threatening a geothermal power plant.

Kilauea’s molten rock, with temperatures at about 1,170 degrees Celsius, is an obvious danger to the local Hawaiian community (one serious injury reported so far). However, the volcanic eruption presents many airborne hazards as well.

In addition to spewing out lava, the Kilauea eruption has projected ballistic blocks, some up to 60 centimeters across, and released clouds of volcanic ash and vog (a volcanic smog of sulfur dioxide and aerosols). The ashfall and gas emissions can create hazardous conditions for travel, produce acid rain as well as cause irritation, headache and respiratory issues.

Kilauea’s lava has steadily marched towards the coast of the Big Island, and recently reached the Pacific Ocean. This interaction of molten rock and ocean water has created plumes of laze (lava haze). Laze is essentially a cloud of acidic steam, mixed with hydrochloric acid and fine particles of volcanic glass. Coming into contact with the toxic vapour can result in eye and skin irritation as well as lung damage.  

Map as of 2:00 p.m. HST, May 31, 2018. Given the dynamic nature of Kīlauea’s lower East Rift Zone eruption, with changing vent locations, fissures starting and stopping, and varying rates of lava effusion, map details shown here are accurate as of the date/time noted. Shaded purple areas indicate lava flows erupted in 1840, 1955, 1960, and 2014-2015. (Image: U.S. Geological Survey)

While residents have been fleeing the the Kilauea-affected region, many scientists have rushed to the Big Island to study the eruption. A swarm of researchers have spent the month recording lava flow activity, measuring seismicity and deformation, monitoring ash plumes by aircraft, and taking samples on foot.

Many volcano scientists have also turned to social media to answer questions from the general public about the recent eruption (like why is the eruption pink? Can you roast a marshmallow with lava?) and bust volcano myths floating online (expect no mega-tsunami from this eruption). The EGU’s own early career scientist representative for the Geochemistry, Mineralogy, Petrology & Volcanology Division, Evgenia Ilyinskaya, was invited to explain some volcano lingo on BBC News.

The volcano’s eruption has been ongoing for weeks, with no immediate end in site. Lava flows are still advancing across the region and volcanic gas emissions remain very high, says the U.S. Geological Survey’s Hawaiian Volcano Observatory. You can stay up to date with the volcano’s latest activity on the agency’s site.  

What you might have missed

A team of scientists from the PolarGAP project have found mountain ranges and three massive canyons underneath Antarctica’s ice using radar technology. These valleys play an important role in channeling ice flow from the centre of the continent towards the ocean, according to the researchers. “If Antarctica thins in a warming climate, as scientists suspect it will, then these channels could accelerate mass towards the ocean, further raising sea-levels,” reports an article from BBC News.

Also in Antarctic news, the Natural Environment Research Council (UK) and the National Science Foundation (US) have announced an ambitious plan to determine the Thwaites Glacier’s risk of collapse. The rapidly melting glacier sheds off 50 billion tons of ice a year, and if Thwaites were to completely go under, the meltwater would contribute more than 80 cm to sea level rise. “Because Thwaites drains the very center of the larger ice sheet system, if it loses enough volume, it could destabilize the rest of the entire West Antarctic Ice Sheet,” according to an article in Scientific American. The research team plans to collect various kinds of data on the glacier and use this information to predict the fate of Thwaites and West Antarctica. The $25-million (USD) joint effort will involve about 100 scientists on eight projects over the course of five years, posing to be one of the largest Antarctic research endeavors undertaken.

Meanwhile, looking out hundreds of millions of kilometres away, scientists have made an interesting discovery about one of Jupiter’s potentially habitable moons.

A team of scientists uncovered a new source of evidence that suggests Europa, one of Jupiter’s moons, may be venting plumes of water vapour above its icy exterior shell. The researchers came across this finding while re-examining data collected by NASA’s Galileo spacecraft, which performed a flyby 200 kilometres above the Europa in 1997. While running the decades old data through today’s more sophisticated computer systems, the research team found a brief, localised bend in the magnetic field, a phenomenon that is now recognised as evidence of water plume presence. These new results have made some scientists more confident that NASA’s Europa Clipper mission, set to launch by 2022, will find plumes on Jupiter’s moon.

Links we liked

The EGU Story

A 2007 paper on global climate zones published in Hydrology and Earth System Sciences, a journal of the European Geosciences Union, has been named the most cited source on Wikipedia, referenced more than 2.8 million times. The Guardian and WIRED reported this story that neither Copernicus Publications nor the Australian authors of the paper were aware of.

EGU training schools offer early career scientists specialist training opportunities they do not normally have access to in their home institutions. Up until 15 August 2018, the Union now welcomes requests for EGU support of training schools in the Earth, planetary or space sciences scheduled for 2019.

In addition, the EGU will now accept proposals for conferences on solar system and planetary processes, as well as on biochemical processes in the Earth system, in line with two new EGU conference series named in honour of two female scientists. The Angioletta Corradini and Mary Anning conferences are to be held every two years with their first editions in 2019 or 2020. The deadline to submit proposals is also 15 August 2018.

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