Borah was rocked at 8:06 a.m., Friday, Oct. 28, 1983 by 7.0 quake. While there has been debate about exactly powerful or important quake was (initial reports had always called it a 7.3 quake), the single most dramatic event associated with it was that Borah when surveyed afterwards increased in height by 7 feet — however even that claim may turn out to be an urban legend.
Richard Carey’s amazing peakbagging.com site has the official National Geodetic Survey history of the Borah Peak benchmark . It’s an amazing tale complete with helicopter visits to the summit (easy to land/difficult to camp). The benchmark dubbed “Beauty” was placed in 1915 reported at 12,655 feet. Mountainclimb.com sent us this photo of the Borah summit benchmark (stamped 12,655).
The benchmark history reports visits since including up to 1967 to check it. Although not mentioned in the article the benchmark was supposedly destroyed in a 1999 lightning strike.
The benchmark history has a reference to a 1986 adjustment after the earthquake placing the height at 12,662 feet (but that height had already been set). There another adjustment in 1992 reflecting that using the new NAVD 88 datum the elevation is 12,668 feet (but using the old 1929 methodology which we use for all elevations here the height would remains at 12,662). Read more about that.
It would seem like a slam dunk to explain the famed 7 foot increase claim.
HOWEVER, the most recent topo map for Borah (1967) listed Borah as 12,662 feet before the earthquake (I’m in the process of looking for the topo before 1967). Further, contemporary 1983 articles list Borah’s height at 12,662 feet. Further the current topo map which was published in 1971 shows Borah’s height at 12,662. Here’s the info on the bottom of the Borah topo.
Here are the articles from the University of Utah history of the quake:
From the Deseret News October 31, 1983:
Portable seismograph stations were set up near the quake’s epicenter, located near Mount Borah, Idaho’s tallest peak at a previous height of 12,662 feet above sea level. There is a 10-mile-long gash on the flanks of the mountain and its sisters in the Pahsimeroi range.
The quake raised the mountain about 15 more feet above the valley floor, but officials said they would not be sure if the valley is lower or the mountain is higher until the area is resurveyed.
From the Salt Lake Tribune October 30, 1983:
Sinkholes, some 10 feet across, pocked the valley floor, caused by liquefaction–the violent shaking of loosely compacted soil until it collapses into a quicksand-like goo.
“Borah Peak [Idaho's tallest mountain at 12,662 feet] could be from one-tenth of a foot to 10 feet higher today,” Wood said. “The valley appears to have dropped about 5 feet.”
Oddly the change in height is not in any of the official writeups of the quake. Dan Robbins Idaho Summits page had a photo of the Idaho Transportation marker which notes “Mount Borah’s ridge front rose about 6 inches while the valley subsided 9 feet”
Zach Vickey sent us a photo of the Borah trailhead which references the 7 foot summit increase.
In any event, my inclination is that the mountain did not grow so dramatically in the quake (mountains traditionally grow by the inch). We will never know for sure until the mountain is resurveyed.
The quake ranks as one of the most powerful earthquakes in the 20th century in the Lower 48 and was the most powerful quake in 23 years. A list of 7.0 or greater earthquakes in the U.S. shows that this writing there have been five bigger quakes in California since Borah. Alaska routinely has bigger quakes. An Idaho geologist in comparing the Borah Quake to the Dec. 26, 2004, 9.0 Summatra that unleashed a tidal wave that killed hundreds of thousands noted that if such a quake occurred it would have traveled all the way to Las Vegas.
The quake was dramatic in that its faulting was up and down (most quakes are not as visible on the fault line as they slide sideways such as the San Andreas where San Francisco and Los Angeles are inching toward each other). The Borah Quake produced a 21 mile long scarp that was raised at points as much as 14 feet and is still visible today. You cross the scarp on the mountain’s west side en route to the trailhead. Ralph Maughan has fantastic photos of the scarp on his Borah page which also includes quite dramatic photos of Borah in winter.
At the time the quake was billed as the most studied in U.S. history. There’s a huge amount online about it.
Official NFS Brochure (which incorrectly lists 7.3 quake but does have maps, etc.)
History of from Geonote
The University of Utah has a huge collection of information on the 1983 Borah Peak earthquake including numerous photos and newspaper articles. The information is presented in a very dry list format. But itâ€™s worth visiting.
Official USGS Write Up
Borah’s earthquake history makes fascinating geology.
The biggest earthquakes in the U.S. are in Alaska and California at the collision of the Pacific and North American plates which are sliding around the world. However there’s a swath known as the Internmountain Seismic Belt which affects Borah. The most dramatic quakes in this band are around Yellowstone National Park which is about 250 miles east of Borah. Yellowstone is actually a supervolcano with a caldera 30 miles across and 45 miles long. Thus as the North American continent slides across the supervolcano it has impacts a U or V shape downstream much as a rock interrupts the flow of a rapid. Borah was the second largest quake in the 20th Century in the Lower 48 outside of California. The most powerful quake was Hebgen Lake, Montana in 1959 which initially listed at 7.5 but has been downgraded to 7.3. Hebgen Lake is part of the Yellowstone impact complex. The only other area in the Lower 48 other than California that is prone to major earthquakes is Missouri but that’s another story and no quakes were greater than 6.1 in the 20th Century. For what it’s worth if you want to get really scared, scientists say Yellowstone erupts every 600,000 years with cataclysmic species-ending intensity with power thousands of times more powerful than traditional volcanos. It’s been 640,000 years since Yellowstone erupted so it’s overdue. Magma is building. The USGS takes it serious enough to have opened a volcanic research station there.
This excellent map from the Utah Geology shows the impact of the Yellowstone supervolcano hotspot on “downstream” areas as the North American plate slides across it. The 20th Century’s two most powerful quakes in the Lower 48 outside of California occurred here. The article (which focuses on the Wasatch Fault) makes fascinating read particularly its photos of short sighted developers and urban planners who think earthquake scarps make cool places for buildings with better views or height elevations.
Posted in Uncategorized and tagged Idaho by Roger with .