In conversation with Dr Kyle Bradley, Principal Investigator at the Earth Observatory of Singapore
1. Can you tell us about your work on geohazards and the interesting parallels between in Southeast Asia and Alaska?
At the Earth Observatory of Singapore, I study the active faults of Southeast Asia and their associated geohazards. We are increasingly aware that rapidly changing environments can produce surprising hazards that can lie undetected for a long time until they are triggered by sudden events like earthquakes or large rainfalls.
Recently we learned about a very interesting geohazard case in Alaska, where scientists have identified a potential tsunami that could possibly be produced by a landslide along the Alaskan coast. Here at the Earth Observatory of Singapore, we are very familiar with tsunamis, as they commonly affect people living along the coasts Southeast Asia. In Southeast Asia, tsunamis are usually caused by undersea earthquakes, and occasionally by undersea landslides.
In Alaska, coastal glaciers are retreating at a rapid pace largely due to climate change. This glacial retreat destabilises the slopes steep valleys that hold the glacier. The rocks and soil that were previously held up against the valley slopes by the massive glacial ice are now perched over the open ocean and are sliding down slowly over time. Any small change could theoretically trigger a landslide of this material into the water, setting off a huge tsunami wave that could wipe out communities in surrounding bays or tourists visiting glaciers by boat.
We know this can happen because it has happened in this region. In 1958, a similar event was triggered by a large earthquake that disturbed a coastal glacier, causing a landslide into a bay. The tsunami that was generated by that landslide removed trees and rocks from the surrounding hillsides up to 500 metres above sea level!
2. Is climate change a contributing factor to this tsunami alert in Alaska?
Coastal glaciers are fascinating geological features, because they are one of the best examples of environmental equilibriums and feedbacks. Glaciers grow or shrink depending on how much of the snow in the source region is preserved over the course of the year. That is mostly controlled by the number of days over the year which are warm enough for snow to melt in the source region, before it can be compacted into glacial ice.
As we know, the Arctic is heating up far faster than the rest of the planet due to climate change. For the first time since records have been kept, open waters are lapping coastlines in many areas of the Arctic as late as October, though snow is already falling. The coastal glaciers now have to adjust to this ‘new Arctic equilibrium’ and the surrounding landscape must also adjust.
When the environmental balance is disturbed rapidly, which is what is happening now in the Arctic, the glaciers retreat quickly, leaving behind all the rocks and sediments that were previously held up in precarious positions. Those rocks and sediments are slowly moving downhill toward the sea under the force of gravity, but we don’t know whether they could also be triggered to fall as a sudden landslide. Geologists are now proposing to monitor and study this region to understand if this can happen, and to possibly build a system that could send out a warning if it does.
3. What lessons can we learn from this tsunami alert?
Here in Southeast Asia we don’t have coastal glaciers, but the lessons we can learn from this case do apply in the broader sense to our region. We see rapid changes in our environments, partially due to human activity such as deforestation, changes in land use, and from global climate change and rising sea levels. These rapid changes have certainly created new instabilities and new hazards in the region, and some of these hazards remain undiscovered. At the Earth Observatory of Singapore, we are working to better understand, plan and mitigate these geohazards in the future.
4. How does your work contribute to a better understanding of these hazards in Southeast Asia?
One good example of how hazards arise from sudden environmental changes comes from the 2018 earthquakes and landslides in Palu, Indonesia. In this area, human change came in the form of irrigation across areas of the Palu Valley that were previously dry. This aqueduct-fed irrigation supported agriculture in a previously unproductive landscape for over a century; however, it also raised the natural water table in an area very close to a large fault line. When a very large earthquake struck on this fault line in September 2018, the raised water table allowed subsurface liquefaction to occur over a wide region that previously would never have experienced this hazard. This liquefaction allowed landslides to form, which moved down the valley floor. These landslides ultimately caused thousands of casualties. Although an earthquake on the fault system was expected, there was little warning of this additional danger because the environmental change (ground water addition) had not been linked to a potential hazard.
In comparison to Alaska where the population is quite remote, here in Southeast Asia we have very dense populations living in environments very close to geohazards. So, it is really critical for us to understand the mechanisms of how landscape changes are predisposing some of these areas to destructive geohazard events. Like in Alaska, we need to identify these unexpected hazards early and come up with proactive plans to study and mitigate them. At the Earth Observatory, we need to continue using basic science research observation with a focus on community engagement, to better understand geohazards and how they affect people, so we can plan for and help build a more resilient future for everyone in Southeast Asia.
(Source of thumbnail image: Francesco Ungaro/Pexels)