[ad_1]
A massive landslide hit the Tyndall Glacier in Alaska in 2015.
Credit: Polar Geospatial Center / 2015 DigitalGlobe, Inc.
A huge landslide and tsunami that have stripped the slopes of an Alaskan fjord could reveal warning signs that can help predict future disasters.
In a new document, researchers described the geological footprints of the tsunami, which devastated the Taan Fjord on October 17, 2015, at an estimated speed of 100 km / h (162 km / h). Using satellite imagery and field measurements, the team discovered that the slope was showing signs of instability for at least two decades before its failure.
"Geological evidence can help [us] understand past events of similar events and could provide a warning, "the researchers wrote Thursday (Sept. 6) in the journal Scientific Reports. [The 11 Deadliest Natural Disasters in History]
The fall
Taan Fjord is located in Wrangell-St. National Park and Elias Reserve in southeastern Alaska. The rugged landscape is dotted with glaciers, including the Tyndall Glacier, which occupied the entire Taan Fiord. Between 1961 and 1991, however, the glacier retreated 17 km to the end of the fjord.
As glaciers retreat and permafrost melts, the rocky hills, once backed by all this ice, become unstable, wrote the research team led by Dan Shugar of the University of Washington and Bretwood Higman of Ground Truth Trekking. The restless nature of Alaska worsens the situation. minor earthquakes regularly shake the walls of the fjord.
These factors may explain what happened in 2015 when a huge stretch of the hill in front of Tyndall Glacier suddenly failed. Fortunately, no human eye was present to witness the disaster, which generated seismic waves equivalent to an earthquake of magnitude 4.9. About 180 billion tonnes of rock and dirt crashed into the fjord, about one-third of the material landed on the glacier itself and two-thirds remained in the water. The resulting tsunami traveled 193 meters (633 feet) across the fjord; in the fjord, it reached 100 meters in many places. After the wave of debris and water that fell, the slopes once covered with 32-meter trees (10 m) were completely stripped.
Signs
It is unclear what triggered the final failure of the slope, the researchers wrote. About 2 minutes before the tsunami, the seismic waves of a magnitude 4.1 earthquake that hit more than 500 km reached the fjord. The shake would not have been much, and that would not have been unusual for the region, the writers wrote, but that could have been enough. Previous months had also been exceptionally wet, which could have further destabilized the slope.
Whatever the reason the slope failed at that time, the landslide was inevitable, the researchers wrote. Satellite imagery revealed that the slope had collapsed since 1996 and that the depressed areas called "grabens", created when the surface of the hill extended downward, had been visible since 1995. For two decades, researchers found were apparent from satellite data.
The researchers found that the deposits left by the tsunami were unique, unlike those left by other modern tsunamis. These deposits formed in three distinct layers, one consisting of fine sands, the other rocks two to ten inches (5 to 25 cm) in diameter and blocks, as well as one final layer consisting of all sanding to rocks 16 feet (5 m) in diameter.
The researchers wrote that seeing these models in a modern and well-documented landslide tsunami provides new clues as to what to look for in the geological archive when searching for ancient tsunamis. The results also suggest ways to monitor unstable slopes as climate change continues to force glacier retreat. The Taan Fjord is remote, but the tidal fjord in the Glacier Bay, Alaska, tourism region experienced a landslide in June 2016. Fortunately, the debris of this event did not reach the Thames Fjord. water, avoiding a tsunami. In the Rink Fjord in Greenland in 2017, a landslide tsunami had a much more tragic result: four people died.
"More landslides are likely to occur as mountain glaciers continue to decline and alpine permafrost thaws," the researchers wrote.
Original article on live science.
[ad_2]
Source link
