Climate Change Behind More Frequent & Powerful Avalanches in Alaska

As global temperatures rise, melting permafrost is expected to cause more frequent and hazardous landslides at Glacier Bay National Park (Source: Glacier N PS/Twitter).

Slow-moving changes to the planet are sometimes difficult to grasp on the human timescale. However, on the glacierized peaks of Glacier Bay National Park in southeast Alaska, entire mountainsides are crashing down in spectacular avalanches and landslides. The culprit? Not the more usual earthquakes, extreme rainfall, or volcanic eruptions but melting permafrost from increasingly warmer than normal temperatures due to climate change.

In recent years, southeast Alaska has experienced notable rock avalanches on top of its glaciers. Rock avalanches involve landslides of fragmented rock that become hazardous due to their large size and ability to travel long distances at rapid speeds. In October 2015, the largest non-volcanic landslide ever recorded in North America occurred on the Tyndall Glacier. Second only to the cataclysmic eruption of Mount St. Helens in 1980, the massive landslide generated a tsunami wave that rose 600 feet, one of the largest tsunami run-ups ever recorded, and stripped alders off the upper reaches of hills on the shoreline.

Just a few months later, a massive rock avalanche spontaneously materialized on the Lamplugh Glacier. Although initially undetected due to its remote location, seismic instruments captured the event as having as much energy as a 5.2 earthquake.

Intrigued by what was happening in Glacier Bay National Park, a team of three geologists from the USGS explored the timing and characteristics of 24 rock avalanches in the park over a 33-year period from 1984 to 2016. Led by Jeff Coe, the recently published article in Landslide documented three distinct clusters of rock avalanche activity during those years: 1984-1986, 1994-1995, and 2012-2016 through the use of Landsat satellite imagery.

Image of Lamplugh Glacier before the 2016 landslide (Source: Allen Castillo/Flickr).

What they found was remarkable: Coe shared the exceptional size of the rock avalanches with GlacierHub. Since 2012, these avalanches were 1.5 to 5.9 times the next largest avalanche in the 33-year sample. The researchers concluded that the avalanches in this third cluster were primarily caused by the degradation of mountain permafrost from long-term warming, in addition to a record-breaking warm spell from 2014 to 2016 in the region. Besides melting permafrost, the study points to other factors such as glacial thinning, increased precipitations, and accumulating elastic strain, as contributors to the weakened slopes.

The increased size and distance of these avalanches appear to be determined more by winter temperatures as opposed to summer temperatures. Coe explains that the warmer than average winter temperatures are behind the weakening rock masses on top of the park’s glaciers, as conditions fail to refreeze as much during colder months as they have previously. As the temperatures warm up to around freezing-melting point in the late spring to summer months, the masses fail and collapse.

In general, climate change is expected to have an adverse impact on slope stability in Alaska. But there has been limited research to assess what changes have already occurred there. This study provides a robust example to systematically study and document the changes in the size and mobility of rock avalanches in Glacier Bay National Park.

Image of Lamplugh Glacier in Glacier Bay National Park, Alaska, taken in May 2018 (Source: Allan Watt/Flickr).

One interesting pattern the team noticed in their work was that 75 percent of the rock avalanches come from slopes facing north or northeast. Coe pointed to another study on the European Alps that could be applied to Alaska. Observing similar patterns during the 2003 summer heatwave, the scientists in the Alps study suggested the north-facing slopes in their research had more extensive rock permafrost compared to the southern slopes. With more permafrost, these north-facing slopes would be more impacted by anomalously warm temperatures.

So far, major avalanches in Glacier Bay National Park have struck remote areas of the park where humans rarely visit. But that luck may not continue. These events are a reminder of the increasing instability of the mountains and risks of disasters.

As was evident with the avalanche-induced tsunami in 2015, danger could strike on both land and in the water. Last June, tragedy struck a fishing village in Greenland when a mountain slope collapsed into a fjord, triggering a 300-foot tsunami wave killing four people.

“Going forward, we suggest that rock avalanche activity in Glacier Bay National Park should continue to be monitored to critically assess our results, hypotheses, and interpretations,” said Coe. If their hypothesis holds and warming temperatures are in fact the cause of the destabilization in these historically cold regions, more high-risk areas for landslides and rock avalanches in less remote parts can be expected.

Roundup: Venezuela, Peru, and the Storglaciären

The Death of a Venezuela Glacier

The Economist: “Venezuela is a tropical country, with rainforest in the south and east, and baking savannah stretching towards its northern Caribbean coast. The Sierra Nevada de Mérida mountain range in the north-west offers relief from the heat. In 1991 five glaciers occupied nooks near their peaks. Now, just one remains, lodged into a cwm west of Pico Humboldt. Reduced to an area of ten football pitches, a tenth of its size 30 years ago, it will be gone within a decade or two. Venezuela will then be the first country in the satellite age to have lost all its glaciers.”

Read more about Venezuela’s Humboldt Glacier here.

The Humboldt Glacier in Venezuela (Source: The Photographer/Creative Commons).

Small-Scale Farmers’ Vulnerability in the Peruvian Andes

From Iberoamericana: “Previous studies have shown that climatic changes in the Peruvian Andes pose a threat to lowland communities, mainly through changes in hydrology. This study uses a case study approach and a mixed qualitative-quantitative method to examine the vulnerability of small-scale farmers in the Quillcay River basin to variations in precipitation and enhanced glacier retreat. The findings of the study show partly contradicting results. On one hand, interpretation of semi-structured interviews suggests a strong relation between climate proxies and increased vulnerability of the smallholders. On the other hand, in the quantitative analysis enhanced glacier retreat seemed to have augmented vulnerability solely to some extent whereas precipitation did not show significant impact.”

Learn more about climate change in the Peruvian Andes here.

Small-scale farmers in the Peruvian Andes sowing maize and beans (Source: Goldengreenbird/Creative Commons).

 

A Glacier-Permafrost Relationship in Sweden

From Quaternary Research: “Here, we present empirical ground penetrating radar (GPR) and electroresistivity tomography data (ERT) to verify the cold-temperate transition surface-permafrost base (CTS-PB) axis theoretical model. The data were collected from Storglaciären, in Tarfala, Northern Sweden, and its forefield. The GPR results show a material relation between the glacial ice and the sediments incorporated in the glacier, and a geophysical relation between the ‘cold ice’ and the ‘temperate ice’ layers…The results show how these surfaces form a specific continuous environmental axis; thus, both glacial and periglacial areas can be treated uniformly as a specific continuum in the geophysical sense.”

Read more about the study at Storglaciären here.

The Storglaciären or “The Great Glacier” in Sweden (Source: SAGT/Flickr).

On Tibetan Plateau, Permafrost Melt Worse Than Glacial Melt

According to a recent study published in the journal Public Library of Science, glacial melt is taking a backseat in the Himalayas to permafrost melt as a central driver of alpine lake expansion and related environmental hazards. This finding is of great importance to policy-makers and communities, who must prepare for flooding and other hazards which can be caused by the expansion of high-altitude lakes.

The study, led by Yingkyui Li of the University of Tennessee, Knoxville in partnership with the Chinese Academy of Sciences, Beijing, determined that patterns of lake changes in the Tibetan Plateau from 1970 to 2010 were more closely associated with changes in permafrost degradation patterns than glacial retreat patterns. This conclusion suggests, at least for this region, the influence of melting glaciers on lake dynamics is outweighed by other environmental processes.

Permafrost is an ecologically important element of high-latitude and high-altitude ecosystems. Permafrost is defined as “perennially frozen ground remaining at or below 0°C for at least two consecutive years,” according to a document on the policy implications of warming permafrost, released by UNEP (United Nations Environment Programme). This frozen soil comprises about 24 percent of the exposed land area in the Northern Hemisphere, and is also found in mountainous regions of South America and ice-free regions of Antarctica. The thickness of permafrost is determined by the distance between the top of the permafrost layer, known as the permafrost table, and the bottom, also called the permafrost base. There may be an active layer above this, which thaws and freezes seasonally. The most robust type of permafrost is continuous coverage, where the permafrost table is very thick and extends for many meters into the soil. Areas with larger gaps in the permafrost can be called discontinuous permafrost zones, or sporadic permafrost.

Current permafrost distribution in the Northern Hemisphere (Photo: International Permafrost Association)
Current permafrost distribution in the Northern Hemisphere (Photo: International Permafrost Association)

 

At the outset of the study, researchers did not hypothesize that permafrost would play an active role in Tibetan Plateau lake dynamics. In order to determine the factors which influenced lakes, Li et al. gathered two sorts of data to assess fluctuations in the elevation of lakes. They used historical altimetry data for 94 lakes across the plateau for 2003-2009, and Landsat imagery data for 25 lakes across five different regions in the plateau for1972-2010. They correlated spatio-temporal patterns of lake change with various climate and environmental variables such as precipitation, evapotranspiration, glacier coverage, permafrost coverage, and daily mean temperature trends.

 

The Tibetan Plateau spans across much of the Asian continent. (Photo: wikipedia)
The Tibetan Plateau spans across much of the Asian continent. (Photo: wikipedia)

The analysis revealed clear spatio-temporal patterns. Lakes in the southern and western plateau showed continuous shrinkage or stable levels except for slight expansion from 2000-2004. Lakes closest to the Himalayas showed evidence of continuous shrinkage. Lakes located in the central and northern plateau seemed to experience rapid expansion after 2000, though data showed slowed expansion after 2006 in the central region. These expansion trends have been confirmed by other studies, including an article published in April 2014; however, the study led by Yingkyui Li is unique in its long time scale and fine-grained analysis of spatio-temporal patterns.

The researchers found, “[there is] no statistically significant correlation between changes in lake levels (2003-2009) and glacier coverage in each lake’s drainage basin.” On the other hand, they were able to conclude, “[the] plateau-wide pattern of lake changes is consistent with the distribution of permafrost on the Tibetan Plateau.”

The mechanism that links permafrost melt with lake expansion rests on temperature regimes in the region. When the ground temperature is lower than the melting point of frozen soil, water contribution of permafrost to lakes is limited because the soil remains frozen. However, higher temperatures accelerate permafrost melt, which contributes to lake expansion. An interesting aspect of this mechanism is when temperatures continuously increase and remain above the melting point; in this case, water contribution once again becomes limited because all water held in the frozen soil has been released. This phenomenon would explain stability in lake levels after rapid expansion such as in the central region.

Gurudongmar Lake, is one of the highest lakes in the world located at an altitude of 17,100 feet in North Sikkim, India. It is located in a plateau area contiguous to the Tibetan Plateau. (Photo: Shayon Ghosh)
Gurudongmar Lake, is one of the highest lakes in the world located at an altitude of 17,100 feet in North Sikkim, India. It is located in a plateau area contiguous to the Tibetan Plateau. (Photo: Shayon Ghosh)

 

Along with the effects on alpine lakes, there are other serious ramifications of permafrost degradation. By releasing water and changing the structure of soils, permafrost degradation can lead to high-altitude lake outburst floods. In mountainous areas, soils can lose their stability as they thaw, creating landslides. Moreover, as shown by a 2010 study, ecosystems which have had historically robust and continuous permafrost can experience reduced productivity and function associated with permafrost loss due to the decreases in soil moisture content and soil nutrients. In addition, the UNEP News Centre has highlighted the permafrost-carbon feedback, in which permafrost loss is associated with emissions of carbon dioxide into the atmosphere; this process could exacerbate rising temperatures.

With these effects in mind, it is important to take into account permafrost changes projected for the future. The UNEP Policy Implications of Warming Permafrost Guide indicates that in the near future “active layer thickness will increase and the areal extent of near surface permafrost will decrease” in most regions. Yet, these changes are contingent upon soil and snow processes, future scenarios of anthropogenic greenhouse gas emissions, and the warming response to increased atmospheric carbon dioxide. If warming continues, eventually the active layer of permafrost, in any region, can become so deep that it does not fully refreeze in winter; this creates a talik, or an area of permanently unfrozen ground within an area of permafrost. In extreme cases, the permafrost can completely thaw and disappear. Clearly, it is important for researchers, policy-makers, and practitioners to take permafrost processes into account if they want protect alpine communities and prevent environmental hazards such as landslides and high-altitude lake outburst floods.