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Mangroves, Mud, and More

September 2nd, 2014 by David Lagomasino

Mangrove forests

Flying over the Colombian Andes from Medellin to Nuqui in a small, 20 passenger propeller plane, five scientists peer out the window to look at the bosque (Spanish word for forest) covering the mountains below for as far as they could see. I was one of those scientists. Dotted throughout the forest, I can see indigenous communities thriving in small clearings with smoke billowing from small fire pits. Then, out of nowhere, the mountains drop off, the Pacific Ocean appears, and the plane banks hard to starboard. Finally! My first glimpse and the reason why I was making a trip out to Pacific coast of Colombia: mangroves.

My first trip to Colombia and I get to see some of the most pristine mangroves in the world. Why am I so excited about mangroves? There is something about the smell of the swamp, the harsh conditions, the incredible resilience of the trees, and the complex hydrology that draws me in. Mangrove is the general term used for a group of salt-tolerant tropical hardwood trees. Large communities of mangroves form unique forested ecosystems unlike any other forest found in tropical, temperate, and boreal climates. Though they only cover 0.1% of the earth’s surface, mangrove forests remove more carbon per unit area than any other terrestrial forest, which in turn, may be extremely important with respect to climate change and increasing CO2 concentrations. Most of that carbon from mangroves is sequestered by the thick layers of organic-rich soil that have been deposited and, most importantly, remains in these environments. Mangroves also provide a number of ecosystems services that can add up to billions of dollars in economic value per year. Some services are obvious like fishing, shrimping, timber and other raw resources. Other services are much harder to value but are still extremely important such as coastal protection, cultivating biodiversity, and cultural services. Despite their economic value or maybe because of it, mangrove forests are disappearing faster than any other tropical environment, including terrestrial forest and coral reef ecosystems, because of deforestation, coastal development and other human manipulations.

My trip was part of Vulnerability Assessment of Mangrove Forests in the Americas, a project funded by NASA’s Land Cover and Land Use Change Program and led by Dr. Marc Simard from NASA Jet Propulsion Laboratory (JPL). The project was designed to identify changes to mangrove forest ecosystems through time and space, and to understand how human activities coupled with land use/ land cover (LU/LC) change have altered mangrove environments. Researchers from NASA JPL, NASA Goddard Space Flight Center, Louisiana State University (LSU), and Indiana University (IU) have visited six sites over the course of the three year study to collect detailed mangrove and socio-economic data. This data is instrumental for developing regional models that can be adapted for diverse communities to assess mangrove vulnerability to human and climate drivers.

Our trip to Nuqui, Colombia was an effort to collect field data in pristine mangrove forests along the Pacific coast of the Americas, a location in which scientists know very little about the extent, height, and condition of the mangroves. The field data, which included tree height and tree thickness, will be used to help calibrate and validate or, in other words, make adjustments to and verify our mangrove structure and biomass models developed using a combination of remote sensing techniques. These remote sensing models use a series of mathematical relationships to estimate such things as tree height, biomass productivity, and carbon sequestration. The other collaborators on the project from LSU collected soil cores while IU initiated a locally-lead program to conduct socio-economic surveys. Fifty centimeter soil cores were collected at each of the sites to determine the amount of carbon found in the ground, which is the largest reservoir for carbon in these ecosystems. Socio-economic activity and demographic information collected from detailed surveys will help us to understand the relationship between the human environment and the changes to the mangrove forests.

Figure 1

(Top left) Skype meeting between NASA JPL interns and researchers from MarViva about remote sensing of mangroves. (Top right) Team America reading about the “Plan de Manejo Manglar.” (Center) Mangrove presentation to the community leaders of Nuqui. (Bottom left) “Mangrove 101” with Edward Castañeda, from LSU. (Bottom right) Team America preparing for meeting with community leaders.

Before any scientific trip to another country, there is a ton of planning and connecting with local agencies to help ensure that you don’t run into any complications. Shortly after our arrival in Nuqui, Colombia, we checked into our hotel and began working on a presentation to show to the local leaders from several small pueblos that comprise the coastal region of the municipality of Nuqui. The presentation was to let the communities know; 1) why we were there, 2) why we are interested in mangroves, and 3) how our research will help the local communities.

The first two points were fairly straightforward. We had preliminary maps from the area which showed us that some very tall, 20-30 meter mangroves were growing in the region. We were there to “groundtruth,” or check out how accurate our modeled tree height estimates were and collect new data to develop better models. Very few studies have investigated mangroves along the Pacific coast and Nuqui was the perfect location to find intact forest ecosystems. Moreover, the coastal communities of Nuqui are dependent on many of the ecosystem services provided by the mangrove forests which include timber/ raw materials, fisheries, coastal protection, and water purification. We tend to forget that we are also part of the ecosystem, and that our actions will have a direct impact on changing the landscape. Nuqui has realized this and has carried out a “Plan de Manejo de Manglar (Mangrove Management Plan)” in the area of Tribugá. The plan includes three “zonas”: de uso sostenible (sustainable use), recuperación (restoration), and preservación (preservation). Mangroves are a necessary part of the coastal Colombian life and rooted deeply into their culture, so much that even the Vice-President of Nuqui, Enrique Murillo-Palacios, was moved to sing about his appreciation for those beloved trees during a dinner we had been invited to.

Mangroves Figure 2

(Top left) Walking home after a long field day in the rain. (Center) Marc Simard, from NASA JPL, measuring tree height. (Top right) Marc Simard showing Hector, from MarViva, how to use the inclinometer. (Bottom left) Cutting soil cores with MarViva and the Vice-President of Nuqui, Enrique. (Bottom right) David Lagomasino, from NASA GSFC, measuring tree diameter above the mangrove prop roots.

We addressed the third objective of our meeting, to show how our research will help the local communities, by working with local community members and local Nonprofits in the field. In addition, we also shared data between groups; some data we collected and other data that MarViva had been previously collecting. Over the course of the field campaign, a handful of local community members and two researchers from MarViva came with us out in the field to collect data. All the groups had their own area of expertise. The locals knew the layout of the land; where the shoals were along the river, where the tallest mangroves were, and a detailed background of the area. MarViva had permanent plots set up at various mangrove sites in the area of Tribugá. And Team America (inside joke: name for the US collaborators of the project) had the expertise in remote sensing, spatial statistics, and mangrove physiology.

While we were out in the field, we showed the locals how to measure tree height using inclinometers, measure tree thickness using diameter tape, and how to collect soil cores. Simple geometry has been integrated into the inclinometer and diameter tape. The inclinometer can estimate tree height by measuring the angles to the base and top of the tree from a set distance from the tree. Two triangles can then be drawn from these measurements using geometric techniques and, voila!: tree height. Old-school surveyors did this all by hand, but nowadays there are fancy inclinometers that integrate all the measurements in a single device with one output… tree height. The diameter tape also integrates geometry by using the relationship between the circumference and diameter of a circle. Collecting soil core tends to be a little more rudimentary, but one must consider a few technical issues first, such as soil compaction and suction, before just hammering a PVC pipe into the ground. From the soil cores we can obtain information about the rate of deposition, the amount of biomass, and the concentration of carbon in the ground. Getting muddy from field work can be one of the best parts of a project. Plus it’s always fun to parkour across a jungle-gym of mangrove prop roots.

Mangroves Figure 3

(Top left) Run-in with a pod of Humpback Whales during our initial site visit. (Top right) Asher Williams and Edward Castañeda, from LSU, learning about a new species of mangroves we had never seen before. (Bottom left) Always, always take a picture of your field book. (Center) Asher admiring one of the only black mangroves (Aviecennia germinans) we came across at our field sites. (Bottom right) Fruit from a mangrove tree.

Edward Castañeda, from LSU, gave an impromptu “Mangrove 101” course to local volunteers while we were taking a break in the field. Professor Castañeda discussed the various physical adaptations that mangroves have developed to cope with the harsh saline environments and remove the high concentrations of salts in the water. Some mangroves can thrive in water with salinities above 90 parts per thousand. That’s almost three times the salt concentrations found in the oceans! There are three main mechanisms that mangroves have developed to allow them to live in salt water: salt exclusion, salt excretion, and shedding. Salt exclusion occurs at the roots where thin membranes prevent salt from entering into the xylem. The excretion technique removes excess salts using glands found in the leaf. You can actually taste and see the salt on the undersides of some leaves. Lastly, some mangrove species can store excess salts in glands from “sacrificial leaves” that fall to the ground, removing the accumulated salts from their system.

Mangroves Figure 4

(Left) Always know where your lines of egress are. (Top) Transportation out of Nuqui. (Right) Marc Simard, from JPL, admiring the mangroves while on a boat ride to our next site. (Bottom) Almost lunch time in town of Tribugá.

After a week of working with the local communities and long days of fieldwork, there were mixed feelings about leaving. Sure, we wanted to get back to hot showers and air conditioning, but being able to see the sites, that we primarily research remotely, we began to formulate more and more questions. What makes the mangroves so big? How does the hydrology influence mangrove communities and tree growth? How deep are the mangrove soils? How far inland to the mangroves extend? Though we may not have an answer for these questions now, it is through collaborations with local agencies and educating local communities that can help us to eventually address research gaps. Town members from Nuqui learned about mangroves and their importance to carbon cycling and MarViva learned about new techniques to survey their field sites. Team America learned much more than we bargained for. Not only did we collect lots of field data for our remote sensing biomass and socio-economic models, but we learned a lot about the culture of Nuqui and how truly important mangroves are in their/our lives.

I stare out into the forest from my perch atop a mangrove prop root, surveying the near-impenetrable entanglement of the forests’ footing. In the distance, calls of “Árbol H6, DAB 4.5, Altura 12 metros” are muffled by the rain. Then I remember that I climbed up here to measure the thickness of the tree… but first, let me take a #selfie.

David Lagomasino

“If there are no mangrove forests, then the sea will have no meaning. It is like having a tree with no roots, for the mangroves are the roots of the sea.”
-Thai Fisherman (Trang Province)

G-LiHT | A View From Above

July 21st, 2014 by Kathryn Hansen

Text by Doug Morton
NASA’s Goddard Space Flight Center

G-LiHT DSLR image of forests and open water near the Tetlin National Wildlife Refuge east of Tok, Alaska. Credit: NASA

G-LiHT DSLR image of forests and open water near the Tetlin National Wildlife Refuge east of Tok, Alaska. Credit: NASA

I have always enjoyed looking out the window of a plane. From the typical cruising altitude of a commercial jetliner, the view of lakes and fields and mountains is familiar (but still fascinating) to a NASA scientist used to looking at Earth from space. Vegetation and land use follow the topography in predictable ways — agricultural fields on the flattest lands and dense forest cover on the warm, south-facing slopes.

Spruce forest in the Yukon-Charley Rivers National Preserve north of Delta Junction, Alaska. Credit: Ross Nelson/NASA's Goddard Space Flight Center

Spruce forest in the Yukon-Charley Rivers National Preserve north of Delta Junction, Alaska. Credit: Ross Nelson/NASA’s Goddard Space Flight Center

In Alaska, the G-LiHT campaign is flying low and slow to provide a very detailed look at forest structure, topography, wetlands, and forest health. At 1,100 feet above ground level, the view from above is stunning. Looking down, you see individual trees, small polygons formed by permafrost, and subtle changes in topography that allow vegetation to flourish on dry ground or wallow in the wetlands of the Tanana flats. Small black spruce trees, barely head high and the width of a dinner plate, are packed together in stands too thick to walk through. Looking out, you can see the vast expanse of the Tanana Valley, a lush green carpet of forest. The braided channels of the river flash in the sunlight as the milky white water heads out of the mountains. Ahead, the steep rise of the Alaska Range signals the end of another flight line.

Seeing the landscape from the same perspective as the G-LiHT sensors provides essential context for the project. The G-LiHT operators on the plane can switch between the real-time view of the incoming data stream and the landscape below. G-LiHT PI Bruce Cook noted, “it’s a little dizzying to watch the imagery fly by on the screen, but matching the bird’s eye view to the data gives an idea of what is possible with the analysis and interpretation of the G-LiHT data.”

Update: As of July 19, the piper had flown more than 70 hours for data collection (9,300 miles), and with more than half of the planned flight lines in the Tanana region completed.

Rainbow over the Tanana River. Credit: Bruce Cook/NASA's Goddard Space Flight Center

Rainbow over the Tanana River. Credit: Bruce Cook/NASA’s Goddard Space Flight Center


NASA’s Alaska Forest Survey Kicks Off

July 14th, 2014 by Kathryn Hansen

From early July through mid-August 2014, scientist Doug Morton of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, will be flying low over the treetops of interior Alaska. The purpose? First-of-a-kind look at the state’s forests with a portable, airborne imaging system called G-LiHT to map the composition, structure and function of the ecosystem.

According to Morton, key components of the fieldwork include:

“First, we are partnering with the U.S. Forest Service, as directed by the recently-passed Farm Bill, to incorporate remote sensing technology into forest monitoring efforts. Our pilot study will be the first inventory of forests in interior Alaska; a standard ground inventory (as in the lower 48) has always been too costly or logistically challenging to implement.

Second, we will study post-fire recovery, with plans to sample more than 80 percent of all fires in the Tanana region since 1950.  Fire is the major agent of change in interior Alaska, and understanding the patterns of forest recovery is essential to gauge the vulnerability/resilience of forests to future climate change.

Third, we will benchmark conditions (topography/permafrost, forest cover, forest composition) across a large portion of the Arctic-Boreal Vulnerability Experiment (ABoVE) science domain.”

Follow Morton through the summer as, Internet connection permitting, he sends updates and photos from the field.



The Pipeline Disaster That Wasn’t

February 5th, 2014 by David Wolfe

Editor’s Note: This guest post was written by David Wolfe, a remote sensing specialist working with the Global Land Ice Measurements from Space (GLIMS) project, and Jeffrey Kargel, a professor at the University of Arizona and the GLIMS project coordinator. Wolfe wrote his thesis for Alaska Pacific University about glacier-dammed lakes in Alaska and recently authored a book chapter on the same topic. Gregory Leonard, Michael Abrams, and Adam Voiland also contributed information for this post.


The Advanced Land Imager (ALI) on the Earth Observing-1 satellite captured this scene of an avalanche in Keystone Canyon on January 31, 2014. Notice how debris has obscured sections of both the Richardson Highway and the Lowe River. Image by NASA Earth Observatory.

On January 24, 2014, an exceptionally large avalanche closed the Richardson Highway (Alaska Route 4), the only land link between the ice-free oil port of Valdez and the rest of Alaska. The avalanche was classified as a size 5, the largest category, though no one was hurt. The avalanche impounded the Lowe River, forming a lake. The lake drained within days of its formation, without an outburst flood, due in part to a 100 year-old abandoned railroad tunnel that shunted water around the dam. On February 5, 2014, officials reopen the road.

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) obtained the image below, on January 29, 2014, upon request by the Global Land Ice Measurements from Space (GLIMS) consortium. The image is an oblique rendering of part of the ASTER image draped over the GDEM2, a global topographic shaded relief map that was produced from a dozen years worth of ASTER images. It is a standard false-color image taken in visible and near infrared wavelengths. Vegetation appears red; snow is white. If clean, water appears black; if slightly sediment laden, it is blue.


Perspective rendering of an ASTER image on a shaded relief map, showing the location of the avalanche and impoundment lake relative to a portion of the Trans-Alaska Pipeline System and Richardson Highway. The image was acquired on January 29, 2014. Image by Gregory Leonard and Michael Abrams.

The ASTER image above shows the outlines of the avalanche source, the avalanche deposit, the maximum extent of the impoundment lake, and the routes of the Richardson Highway and the Trans Alaska Pipeline System (TAPS). The lake had partially drained when the image was acquired. At maximum extent, the lake apparently barely overlapped part of the route of the pipeline, but in this sector the pipeline is buried and was thus safe. Although the greater potential pipeline disaster was averted, the closure of the highway has been a significant inconvenience for many people in and near Valdez. Ferries into and out of Valdez were increased to assist stranded residents, and roadway commerce as far as Fairbanks must have been affected by the disruptions to the Richardson Highway.



Crews from the Alaska Department of Transportation and Public Facilities (ADOT&PF) mobilized equipment on the south side of the road closure Thursday evening, January 30, 2014, and began 24-hour snow removal operations early Friday. The top photo shows a Hitachi 450 excavator, providing a scale that shows the avalanche to be 40 feet (12 meters) thick at this location. The next photo, just above, shows a daytime view of the night-and-day operations to reopen the highway. Elsewhere, reports have the avalanche approaching 100 feet (30 meters) thick. Photos courtesy of Robert Dunning and staff, Alaska DOT&PF, reproduced by permission.

The 1.35 square mile (3.5 square kilometer) source of the avalanche was estimated from the ASTER and ALI images and from news broadcast video taken from a helicopter by ADOT&PF, Alyeska Pipeline Service Co., the Anchorage Daily News, and Alaska Dispatch staff. The huge avalanche and 0.135 square mile (88-acre, 0.35 square kilometer) impoundment lake reminds us of the remarkable engineering of the Alaskan pipeline (below). The pipeline faces many natural hazards, including earthquakes, landslides, floods, forest fires, avalanches, glacier lake outburst floods, and thawing permafrost. In 2002, it survived the magnitude 7.9 Denali earthquake without rupturethough  just barely. Several key design tolerances were closely approached or exceeded, according to a report published in Earthquake Spectra. That earthquake and the 2014 avalanche did not cause a disaster because of the pipeline’s careful engineering, including the use of many novel technologies and special routing. Just about 1.9 miles (3 kilometers) upstream of the Lowe River crossing, the highway and pipeline traverses a creek that has been inundated by periodic outburst floods, some destructive, from a series of glacier-dammed lakes high in the mountains. TAPS was routed underground through the flood impact zone and over the Chugach Mountains. The specific routing averted the extent of the avalanche and lake with no room to spare, suggesting an element of good luck.


Figure 4. TAPS south of the Alaska Range, highlighting several innovative design features of the TAPS, including the burial of the pipeline in some sectors (such as here, where the pipeline goes underground), the elevation of the pipeline in other sectors, passive ammonia cooling system to maintain the frozen permafrost, and the zig-zag pattern designed to absorb earthquake-caused deformation. Photo courtesy of Jeffrey Kargel.

A larger view of the full ASTER image acquisition is shown. Note the presence of unfrozen sediment-laden glacier meltwater of the glacial lake (cyan) north of the oil port and east of the city of Valdez.  The unfrozen state of the lake in mid-winter is a testament to the unusually warm January in Alaska.



The upper image is an ASTER RGB false-color composite image draped onto the GDEM2 shaded relief map that shows the broader area.  The town of Valdez is visible along the eastern arm of the Valdez Arm.  Valdez Glacier, with its terminal lake (cyan), is visible northeast of the city. The lower image is an inset that shows the site of the avalanche in more detail.

This winter has been extremely mild in Alaska, enough for the record books, and the weather data point to the likely trigger of the avalanche. National Oceanic and Atmospheric Administration (NOAA) records indicate the January 2014 snowpack for the Valdez recording station was far below normal, while the amount of precipitation (rain or snow-water equivalent) received was more than double the January normal since 1972.  The huge avalanche was conditioned by three consecutive days of record high or record high minimum temperatures and then triggered by days of record anomalous rainfall.

January 2004 temperature records for the Valdez recording station. The almost horizontal lines are the averages for those dates (“normals”) over the period 1972-2014. January 2014 was twice as wet as normal, and about 6°F (3.3 °C) warmer than normal, but the day of the disaster and three preceding days broke multiple weather records in several parameters. Daily low temperatures (not shown) were also exceptional, with no freezing conditions in Valdez for the three nights prior to the avalanche, whereas normal lows are about 19 degrees for those dates.

January 2014 temperature records for the Valdez recording station. The almost horizontal lines are the averages for those dates (“normals”) over the period 1972-2014. January 2014 was twice as wet as normal, and about 6°F (3.3 °C) warmer than normal, but the day of the disaster and three preceding days broke multiple weather records in several parameters. Daily low temperatures (not shown) were also exceptional, with no freezing conditions in Valdez for the three nights prior to the avalanche, whereas normal lows are about 19 degrees for those dates.

A sequence of exceptional weather anomalies extend back to October.  That conditioning set the stage for the rainfall trigger to release the huge avalanche. The warm weather across most of Alaska—including an Arctic January in Kotzebue that experienced winter temperatures more typical of those in Portland, Oregon, is the other side of the coin that dealt the U.S. East, Midwest, and South a severe deep freeze.  Such extreme oscillations of weather are related to a deeply dipping jet stream and establishment of a days-long flow of saturated tropical air into the Valdez area. These conditions, particularly the strong meridional flow of air masses and “stuck” jet streams that resulted in prolonged extreme weather patterns, are thought to be increasing in frequency due to global warming, according to climate modeling by Jennifer Francis (Rutgers University) and colleagues.  The Arctic is warming more rapidly than the Tropics, which may be forcing changes in global circulation and weather patterns.

However, decadal variability caused by atmospheric and oceanographic “teleconnections” to the rest of the planet (El Niño/La Niña being the most famous example, and the Pacific Decadal Oscillation being the one most relevant to southern Alaska) are always causing climatic oscillations and sometimes extreme weather, so we cannot yet point definitively to climate change, as opposed to these oscillations, as the underlying cause of this event.  These climatic oscillations affect everything from the salmon fisheries to snowfall and rain patterns, so climatologists will have to look deeply at global warming, disappearing sea ice in the Arctic, and climate oscillations to find the ultimate answer to why Alaska’s weather has been so weird (and indirectly, why this mega-avalanche occurred), and how that relates to what is happening around the globe.

Figure 7. GOES-15 satellite image at 6.5 microns(a region of the thermal infrared that is absorbed by water vapor), portrayed as the temperature at the top of the water-vapor emitting region (clouds or humid air). Reds and yellows portray a very dry atmosphere, where emission of thermal infrared arises very deep in the atmosphere at high temperatures; blues indicate a moister atmosphere, and white and green an extremely moist atmosphere extending to very high altitudes having very low temperatures. The image was acquired 3:00 PM (local Alaska Time Zone) on 23 January 2014, the afternoon before the giant avalanche. A stream of extremely moist air arising in the northern Tropics—sometimes called the Pineapple Express—had been slamming into the Valdez and Keystone Canyon area (red square) for several days, thoroughly soaking the area. Valdez received over 11 inches of rain in the 12 days preceding the avalanche. Image rendered and made available by the Cooperative Institute for Meteorological Satellite Studies (CIMSS), University of Wisconsin – Madison, USA.

GOES-15 satellite image at 6.5 microns (a region of the thermal infrared that is absorbed by water vapor), portrayed as the temperature at the top of the water-vapor emitting region (clouds or humid air). Reds and yellows portray a very dry atmosphere, where emission of thermal infrared arises very deep in the atmosphere at high temperatures. Blues indicate a moister atmosphere, and white and green an extremely moist atmosphere extending to very high altitudes having very low temperatures. The image was acquired 3:00 PM (local Alaska Time Zone) on January 23, 2014, the afternoon before the giant avalanche. A stream of extremely moist air arising in the northern Tropics—sometimes called the Pineapple Express—had been slamming into the Valdez and Keystone Canyon area (red square) for several days, thoroughly soaking the area. Valdez received over 11 inches of rain in the 12 days preceding the avalanche. Image rendered and made available by the Cooperative Institute for Meteorological Satellite Studies (CIMSS), University of Wisconsin – Madison, USA.

The avalanche in Alaska cannot be blamed squarely on climate change, but it is another reminder that as climate changes, extreme weather may also be changing, and this impacts the well-being of people and critical infrastructure. Climate change and effects on natural hazards and disasters represents a moving target that must be re-examined by those planning the future, whether it is construction of major infrastructure or planning for disaster recovery. Climate change is not just a matter for the distant future, but it is ongoing now.

We thank the NASA Cryosphere Program, which funds our glacier and cryosphere related research, and the U.S.-Japan ASTER project, which provided the ASTER imagery.

Editor’s Note: Jeffrey Kargel is a hydrologist at the University of Arizona and for the Global Land Ice Measurements from Space project. This is his account of the research he did during the aftermath of a deadly flash flood in Nepal’s Seti River Valley to determine its cause. You can read more about the event here.


Silt and gravel deposits trace the path of the 2012 hyperconcentrated slurry flood, which ravaged Kharapani village, shown here. Annotations show where people died and where they survived. Our research group has undertaken a detailed demographic and sociological investigation of the losses and survivors all along the devastated parts of the Seti River. The panel at lower right was a 1-year anniversary meet-and-greet commemoration, where we met survivors, media, and politicians still very much concerned about the disaster. (Photos courtesy of Jeffrey Kargel, University of Arizona.)

On May 5, 2012, I was attending a conference at ICIMOD (the Kathmandu-based International Centre for Integrated Mountain Development). I heard about the terrifying disaster that day. A flash flood—what geologists call a hyperconcentrated slurry because it was thick with suspended silt—had torn through some villages along the Seti River, in north-central Nepal, just north of the country’s second largest city, Pokhara. It was immediately recognized as a very deadly event, but the death toll—and a tally of those who remain missing but were clearly also killed—was not known exactly for several months. Seventy-two souls lost. Though not large on the scale of global disasters, this event was terrifying for the fact that it seemed to come from nowhere—literally from beneath a blue sky. Furthermore, there was no immediately evident cause. Nobody and no camera captured the whole event, but there were bits and pieces that had to be spliced together, and missing parts of the story had to be built from the ground up—literally from the rocks and sediment involved in the disaster.


The source area for the avalanche of May 5, 2012. Annapurna IV is just off image to the upper left. The rocks here are layered metamorphosed sedimentary rocks deposited originally in the Tethys Sea before the Himalaya rose; the rock layers are now tilted up. Ice hangs precariously at the ridgeline, and apparently an icefall started the whole messy disaster. A dust cloud lingers from a small debris fall just moments after we first landed in Sabche Cirque 6 months after the disaster. (Photo courtesy of Jeffrey Kargel, University of Arizona.)

Seeing that the disaster occurred at the foot of the Annapurna Range, within the Greater Himalaya, probably every expert’s first thought was “glacial lake outburst flood” (GLOF), because these were common in Nepal’s Himalaya, and the news accounts of the disaster event resembled accounts of GLOFs from other parts of the country.  It took me 10 minutes to examine recent satellite imagery enough to see that there were no lakes, at least not in the images I examined, that could have burst out like this.  So either there was a hidden glacial lake somewhere—maybe under the glacier ice—or a glacial lake developed very rapidly and then drained that tragic day, or—far more probable—this was not a GLOF at all.  It was, however, clearly a disaster that had its source in a high Himalayan amphitheatre-like bowl, a glacially-carved structure called the Sabche Cirque. This structure was rimmed by some of Nepal’s most famous, picturesque mountain peaks, including the storied, holy Machapuchare (the “fishtail” peak) and Annapurna IV, a 24,688-foot (7525 m) soaring metamorphic buttress of metamorphic rock.


View of the avalanche deposit of rock and ice shed from Annapurna IV, which is just beyond the upper right corner. (Photo courtesy of Jeffrey Kargel, University of Arizona.)

One of the most important pieces of information on the cause of the disaster was obtained from wingtip cameras mounted on a tiny 2-seater tourist plane.  The pilot, Captain Maximov, had observed what was obviously a giant avalanche—bigger and browner than any snow avalanche he had ever seen before; he then he saw a massive flood wave pouring down the Seti River valley.  It was evident immediately that this brown cloud of roiling airborne debris was connected to the trigger for the disastrous flood.

This distant view provided in the tourist plane’s video, in addition to later observations I was able to make from the Sabche Cirque itself, led to a confident sourcing of the brown cloud and the disaster’s trigger on a ridgeline near Annapurna IV.  Apparently part this ridge—probably initially the glacier ice— collapsed, dropping ice and rock over 3000 m almost vertically (about 10,000 feet) onto unconsolidated rock debris (glacial moraines and ancient glacial lake silts and gravels) resting unstably in the deep bowl of the Sabche Cirque.  Some of that loose debris was also swept up by the avalanche, and the mass flowed an additional 1,500 meters (about 5,000 feet) into the Seti River gorge.


Ancient glacial lake sediments such as these in the Sabche Cirque were swept up by the avalanche and ingested both into the ground surge and airborne cloud, then ingested into the reservoir, which then burst forth onto unsuspecting people below.(Photo courtesy of Jeffrey Kargel, University of Arizona.)

The triggering avalanche—though enormous and bigger than almost any normal avalanche—was the easy part of the explanation of the disaster.  The hard part was identifying the source of the water, because there was no glacial lake or no known lake at all in the area.  Somewhere a large amount of water had been stored and then suddenly released. Speculation centered on water contained within unseen and unknown caves, or within the deep gorge of the Seti River, and last of all, possible subglacial lakes or lots of little ponds that acted like one big lake. This flood appeared to behave like a glacier lake outburst flood, and the news media can be pardoned for having assumed that it was. From that first day, I and other experts tried to counter the media view that it was a GLOF, but anyway, it was a lot of floodwater.

Since I was in Nepal, I immediately contracted for a helicopter to fly me and some colleagues over the Sabche Cirque. We observed directly evidence of the avalanche—boulders and dust and snow-like pulverized ice in a huge sheet, and streamers of debris emanating from the base of Annapurna IV to the head of the enormous Seti River gorge. We helicoptered over the glaciers and found some small ponds, but nothing that could explain the volume of water; and besides, the ponds were in the wrong place to have been strongly affected by Annapurna IV’s ice/rock avalanche. The pathway of the avalanche became ever clearer after post-disaster Landsat and ASTER images showed clear details of the avalanche deposits.


The avalanche route through the upper gorge. (Photo courtesy of Jeffrey Kargel, University of Arizona.)

Speculation was now focused toward the gorge. Could something have blocked it?  Well corroborated resident eyewitnesses interviewed by our team indicated that one to three weeks prior to the disaster, the Seti River had slowed to a mere trickle of clean water, unlike the usual turbid, sediment-laden “glacial milk.” (Seti means white, so it is the White River.)  These various observations and ideas had already started to coalesce when my assistant, Greg Leonard, observed a speck of change that had occurred in “before” and “after” ASTER satellite images.  We had a specific spot to look for a rockfall into the gorge.  Then looking at our helicopter-borne photography, we found it. It was indeed a fresh rockfall straight into the gorge, right at a place from which it appeared a backed-up reservoir had issued a flood. Furthermore, Greg showed that the gorge had experienced many smaller rockfalls or other erosional events over the previous decade, but this bigger one seemed to be fresh. The gorge now seemed the likeliest culprit, but at first it seemed difficult to comprehend how much water could be stored in the gorge behind a rockslide dam.


Flattened forest blown down by the avalanche winds. (Photo courtesy of Jeffrey Kargel, University of Arizona.)

In the days after the disaster, I examined amateur video of the event taken from Pokhara, a couple dozen kilometers downstream from the gorge. I watched as the flood reached Pokhara and as floating trees trunks poured over a dam. It provided the first best opportunity to measure the speed of the floodwaters and its depth and width, and thus measure the volume rate of flow and estimate the total flood volume. The flood came in waves, and the first wave alone was around a quarter of a million cubic meters in just a few minutes. There were about 27 waves in all over the next hours, according to eyewitnesses, so several million cubic meters overall.

At first it seemed a stretch for any one of the suggested water sources to explain the water volume, and this still is a part of the challenge to provide the full explanation of this event. Even my grandson, also intrigued as well as horrified by the disaster, brought his 7-year-old intellect to bear and suggested that it was friction that melted snow and ice that had tumbled off the peaks. Indeed, the conversion of gravitational potential energy to heat could have melted roughly a tenth of the falling snow and ice by the time it reached the Seti River. Nothing seemed quite sufficient; every potential source at first appeared an order of magnitude insufficient to explain the water volume. It seemed that all of the possible sources together might explain the floodwater volume.  Yet one source seemed to be definitely involved, and that was a rockslide-dammed reservoir in the gorge.


A view of the gorges and also the distant peaks of the Sabche Cirque and the ancient glacial deposits in between. The avalanche entered the gorge from the upper right corner of the scene.

I returned with colleagues to the Sabche Cirque three more times, and we were able to land and set up camp and undertake detailed geological observations. The Sabche Cirque is a violent but beautiful place, with rockfalls, snow and ice avalanches, and flood dangers abounding, and evidence of big and recent geologic activity everywhere we walked or flew. We sampled and later chemically and mineralogically analyzed the dust fallout from Captain Maximov’s brown cloud, and linked it to the sediment deposited by the flood on the ravaged villages downstream. We analyzed the bedrock, the boulders of the avalanche, and searched for other evidence of floods and debris flows. That evidence is everywhere. However, the more we searched, the more it became evident that this was definitely not a GLOF, but was caused by a rockslide into the Seti River gorge, formation of an impoundment reservoir over a several week period due to damming of spring snow and ice melt, and then the final triggering event of the mighty rock and ice avalanche off Annapurna IV. On our most recent trip we used a laser device to determine the depth and width of the gorge and discovered that it is so immense that it alone might account for the required water volume.


Our first view of the rockslide that initially dammed the Seti River some weeks prior to May 5, 2012, and set the stage for the deadly terror. (Photo courtesy of Jeffrey Kargel, University of Arizona.)

Although this was a terrifying and deadly event, by geologic standards it was not particularly huge. The death toll was due foremost to people living in harm’s way on the lowest terrace and even on the lowest floodplain. Our findings do not bode well for the future of the small settlements scattered along the riverside, and there would seem to be a strong case for resettlement.


Another devastated area, where there were losses and survivors. A year after the disaster, we were surprised to see a woman living in a house that had barely escaped destruction. Her husband was a river worker. Cattle were grazing nearby. Survivors told harrowing and heart-breaking stories of their tragic losses. (Photos courtesy of Jeffrey Kargel, University of Arizona.)

ACKNOWLEDGMENTS.  This sequence of events was pieced together from many data sources, and many people were involved, among them my colleagues and myself, but also Captain Maximov, local villagers, landslide blogger David Petley and his associates; research staff and my field assistants from ICIMOD, especially Sharad Joshi; my other Nepalese colleagues, including Dr. Dhananjay Regmi and Dr. Lalu Poudel; our chief climber, JB Rai and his Sherpa assistants; and two doctoral students, Khagendra Poudel and Bhabana Thapa, who are investigating the geomorphology and sociology of the disaster. I also need to give special thanks to my tireless assistant, Greg Leonard, who was the prime satellite image analyst as well as my chief field assistant.  Finally, I express gratitude to the NASA/USAID SERVIR Applied Sciences Team,  NASA’s Cryosphere Program, and the USAID Climber Science Program, who funded different aspects and phases of this work, and the U.S.-Japan ASTER project, which provided the ASTER imagery. This work will be presented in more complete detail within an upcoming peer-reviewed scientific publication.


A mosaic of images showing the rockslide area in the foreground in the glacial sediments and avalanche route in the background. (Photo courtesy of Jeffrey Kargel, University of Arizona.)


Notes from the Field