A magnitude 7.0 earthquake that struck Dec. 6 near Yakutat resulted in dozens of massive avalanches, scientists say.
Scientists are calling it the Hubbard Glacier Earthquake , since it happened under that particular glacier located in the Saint Elias Mountains in Canada, just north of the border with Alaska. There is some interesting geology surrounding the quake and its impacts, including the number of landslides and avalanches it triggered, its location being in the Fairweather Fault system, how shallow the quake was, and the aftershocks.
started gently and then remained strong throughout the remainder of the quake, which he called long and ongoing. “I initially thought maybe something was going on in the house. Maybe the kids were active or something like that, but then it kept going,” Valle said. “In the time it took me to get up and walk to the other room, we started having sort of a major shake start taking place.” He said usually things start to jump around during quakes, but that wasn’t his experience with the Hubbard Glacier Earthquake. “This time it was more of swinging side to side rather aggressively. And the ornaments on the Christmas tree were going nuts,” Valle recalled. “We have an extensive Lego collection in the house, and that was rattling around.”miles from the epicenter, didn’t feel shaking quite as intense when the quake hit. “I could see my chandelier, and it started swaying back and forth, and then, I have a bunch of bottles on my windowsill, and they were all rattling, and the couch, of course, was starting to shake back and forth, and pretty much knew it was an earthquake,” Benner recalled.The United States Geological Survey notes it had a depth of only about six miles, and a quake is considered shallow if the depth is less than about 44 miles. The Alaska Earthquake Center said since it was a shallow quake, the “ground shaking was very strong in a 50-mile radius of the epicenter.” “When the fault is closer to the surface, the shaking has less time to kind of attenuate because the fault is just very close,” explained USGS Research Geophysicist Kate Allstadt. “So when you have a deeper earthquake, the shaking has to travel through a larger depth of rock, and that makes the shaking weaker by the time it gets to the surface."“It appears to be generating a pretty vigorous aftershock sequence,” said Michael West, state seismologist with the Alaska Earthquake, within an hour of the quake.For shallow quakes like the Hubbard Glacier Quake, Austin Holland, Alaska Earthquake Center’s operations director, said scientists generally expect very significant aftershocks. As of Dec. 12, he recalled there were more than a hundred magnitude 4.0 or higher aftershocks and a few that were magnitude 5.0 or greater. “There’s a lot of readjustment, especially in complex fault systems like this,” Holland said. “You can have these very strong aftershock sequences where there’s a lot of rebalancing of the stresses within the earth occurring.” He said they try to track all the aftershocks, but it gets difficult to count when there are so many. “It continues to just have earthquake after earthquake. It’s interesting,” Holland said. “It’s so many aftershocks that many of them are occurring basically right on top of each other, and it becomes very difficult to even process the earthquakes themselves because of the signals become intertwined.”Hundreds of landslides and avalanches are thought to have resulted from the shaking.“The USGS mapped about 700 different locations that had characteristics that were consistent with some sort of either landslide or snow avalanche,” Allstadt said. USGS used a remote sensing technique that uses radar to see the landslides and avalanches. Because it has been cloudy, a lot of snow fell, and the daylight hours are limited, Allstadt said. “A lot of them are probably snow avalanches because they were having a blizzard around the time the earthquake happened, and also afterwards, and there were lots of aftershocks,” she said. “Some of them, especially some of the smaller ones, are probably snow avalanches, but we know for sure that at least a few of the really big ones involved some rock.”“The contrast was very different from before to after, and so, we can mostly see the deposits of the snow, the rock and the ice onto these glaciers,” she said.“Usually when the magnitudes are larger, and the fault is near the surface, and it’s in a mountainous area, we typically expect quite a bit of landslide activity,” she said. “There’s been quite a few earthquakes in the past in this part of the world that have had similar behavior, like the Denali earthquake in 2002, triggered thousands of landslides. The 1964 Great Alaska earthquake triggered a huge number of landslides, some of which are similar in character to the ones triggered by this recent earthquake.”“I think the longest one that we measured was about four miles long at least,” she said. The radar technique makes it hard to see the entire landslide and where it came from, so she said some of them could be even longer, and more data will help determine that. She said one of the larger landslides USGS mapped was on the flanks of Mount Logan, which is the tallest mountain in Canada at 19,551 feet. Quite a few of the landslides that were measured, including the longest one, were on the same massif as Mount King George, a famous landmark in Canada.“It’s an extremely remote area that’s just filled with these massive glaciers. So, none of the areas I looked at seem to be close to any place where there could be impact. It is possible you can get smaller landslides further away from the earthquake fault and from the epicenter,” she said.The quake happened on a fault in the Fairweather Fault system, which is known for producing an earthquake in 1958 thatMORE: Can something like what happened in Lituya Bay happen in Southcentral Alaska? Holland said the Fairweather Fault system is a “complex faulting area” that is known for its potential for significant earthquakes, like the Hubbard Glacier Earthquake.“While we are currently calling it a rupture on one of the northern strands of the Fairweather Fault System, it’s worth noting that in 2010, then-graduate student Julie Elliott at the University of Alaska Fairbanks called the section that ruptured today the Connector Fault. The National Seismic Hazard Model picked up this name in 2023,” the Alaska Earthquake Center wrote about the quake the day it happened. “It is definitely not a single location on a map. It’s a large area of rocks sliding past each other with great force,” Holland said. “It is a complex geologic area with a lot going on,” Holland said. “Certainly, these earthquakes remind us that this is an active fault system capable of producing large, crustal earthquakes, and they can have very significant consequences.”It’s definitely not the first time something like this has been recorded. Allstadt said the 2002 Denali Earthquake was also under a glacier.“We don’t know the geometry of the faults in this area very well,” she said. “A lot of earthquake geologists want to know, ‘Did it rupture the fault, and where was it, and can we learn something more about the tectonics of Alaska here?’”Yukon Geological Survey did reconnaissance flights on Dec. 12 to look for fault rupture on the surface of the glacier, which would look like a large crack or separation in the ice. She said the Yukon Geological Survey did not find evidence of a surface rupture, “but I would say that doesn’t rule out surface rupture because we have that fresh snow,” which could cover the evidence, she said. Allstadt said if there was a surface rupture, it would likely not cause a dramatic change to the glacier when it comes to its future. “I’m sure the glaciers, something about them would be altered, but I think the total offsets are fairly low,” she said. “What could have a more dramatic change is the material from landslides,” she said. “If you have darker material on a glacier, depending how thick it is, it can either insulate the glacier or it can cause it to melt faster.” “We certainly try to learn from each event as much information as possible. So, to understand, ‘What does a significant shallow earthquake do to a glacier and its behavior?’ We don’t necessarily have all the answers of what this might look like for the Hubbard Glacier,” Holland said.Off duty trooper, family chased in Wasilla road rage caseMat-Su Republicans become lawmakers after legislative body shifts $1.36 billion for rural healthcare comes with catch: Alaska must pass laws lawmakers say they weren’t briefed on‘Have fun, stay safe and, if you are going to be using alcohol, please don’t be on the roads’
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