The Cascadia subduction zone in the Pacific Northwest is known for two things - earthquakes and tsunamis. Most people, however, are unaware that most of the damage from a magnitude 9 earthquake will be from landslides. Despite this looming threat, there is a general lack of understanding of how earthquakes affect the landscape in the Pacific Northwest. The last major fault rupture occurred on January 20, ; the earthquake lowered the coastline and unleashed a tsunami that reached Japan. However, no single landslide from that earthquake has been definitively pinpointed. In the Oregon Coast Range, there are greater than 30, large bedrock landslides; yet, none of these landslides have been historically observed, though shallow landslides and debris flows abound in the rainy season each year.
Dec 23, Radiocarbon dating of landslides near the deadly March mudslide in Oso, Washington show that this is a geologically active region, with . Nov 08, Radiocarbon dating, where carbon from landslide organic material is compared to the modern atmosphere, is a common landslide-dating technique. Other researchers have measured the surface roughness of landslide surfaces to estimate the time of failure. Early work based on dendrochronology and radiocarbon dating suggested the landslide occurred between AD and or between and The year has often been cited as the date of the Bonneville landslide. More recent work using radiocarbon dating and lichenometry has suggested dates between and or between and
Where these lakes form, they drown Douglas-fir trees. Given these trees died synchronously with the landslide, the tool of dendrochronology, or tree ring science, provides the means necessary to date the landslide. Collected slabs, or wedges, from Douglas-fir snags at landslide-dammed lakes.
Ring width variations record climatic forcings such as drought, as visible on the right. For example, several small rings beginning in correspond to regional drought that is visible in tree rings throughout western Oregon. The end of the ring record here corresponds to tree death in In order to date a landslide-dammed lake, we collect slabs from the standing trees for analysis.
We sand and polish the slabs to a brilliant shine, taking off material as small as 12 micrometers, and using high-resolution scans, we measure the rings on all the slabs. Since we are not interested in how old the trees are, but the year in which they died, we cannot simply count the rings.
We must compare the ring widths to a known record. Fortunately, dendrochronologists devote much of their time to building tree ring chronologies from live trees: records of ring growth that are high-precision records of climate, particularly drought. If we have prepared and measured our slabs well, and there is overlap between the measurements and the chronology, we find a date!
To get an age for the valley's landslides, LaHusen and colleagues, including Alison Duvall, also at the University of Washington, started by dating plant material in the Rowan and Headache Creek landslides, just downstream and upstream of the event, respectively. They found that the Rowan Landslide - approximately five times the size.
Our work to date landslides in the Oregon Coast Range using Douglas-fir tree rings has so far resulted in two landslide ages. While neither of these landslides formed in the year during the last earthquake, our dates are noteworthy due to their ukeitaiplus.comecedented accuracy.
Ward Thomas - Landslide [Fleetwood Mac Cover]
Dating a landslide with radiocarbon methods often results in an error spanning a year period. Some have claimed that they have dated landslides that correspond to the earthquake, though none have circumvented the error that distorts their landslide ages.
We have found at Wasson and Klickitat Lakes that while radiocarbon dating may suggest that is a possible date for the landslides, tree ring data negate such a possibility.
So, while radiocarbon dating is useful and can help narrow the range of possible ages, it is currently not possible to date a landslide with the sub-annual accuracy common to dendrochronology.
As the people of the Pacific Northwest confront the hazards posed by the Cascadia subduction zone, they must consider the threat of landslides in steep terrain, in addition to the hazards of ground motion and tsunamis. As landslides in the Oregon Coast Range continue to be dated, and potentially connected to previous earthquakes, communities must utilize these improved hazard assessments.
Bio Latest Posts. I study ancient landslides in the Oregon Coast Range, hoping to determine how common landslides were during the last major subduction zone earthquake. But they may also be used to date adjacent slides, LaHusen says, as newer landslides tend to have rougher surfaces, which then smooth out over time due to erosion.
The technique allowed the team to determine approximate dates for the remaining slides in the valley without having to radiocarbon date each one. The researchers found that many of the Stillaguamish slides were younger than expected, less than 2, years old, meaning that landslides have been occurring more frequently in recent times, perhaps as often as every years on average instead of every years.
Landslide definition, the downward falling or sliding of a mass of soil, detritus, or rock on or from a steep slope. See more. A landslide inventory is made using the Landsat Archive (-). Cumulative difference of NDVI and a harmonic fit is used to detect landslide timing. Timing of respectively 80and 85of the landslides was determined using CDNDVI and dCDNDVI. Mean dating errors decreased after detrending CDNDVI. Using individual dating methods and landslide elements for timing landslides. (A) The proportion of individual methods used for landslide dating in studies before and after the year Author: Tomas Panek.
Geological Survey in Vancouver, Wash. However, he says, the surface roughness technique needs more testing to establish its validity as an absolute dating tool. The next step should be to test the technique in a different location where a lot of landslides have occurred simultaneously, such as during a big earthquake, he says.
The team did find evidence, however, for a pattern that might provide clues as to where the next slide could take place. As the river erodes laterally into the glacial material, it destabilizes [valley] walls, leading to slides.
Landslides of sufficient volume in turn block the course of the river, forcing it to the other side of the valley. LaHusen says a team led by Adam Booth at Portland State University plans to expand their study throughout the entire kilometer-long river valley, which shows signs of more than slides, to look at patterns in how the landscape is evolving.
Or occur at certain intervals? These are patterns you can only tease out when you look at a larger area.
The landslide dating confirm
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