Sunday, November 03, 2013

It's My Fault

Some people think it's strange that I continue to keep a close track on earthquakes, even though I'm in Idaho. But it's kinda cool to be one of the few in Idaho who knew about the loss of the rubber duckie created by Dutch artist Florentijn Hofman after the pump faltered during a late October quake in Taiwan. But beyond that, southern Idaho actually has its own little "ring of fire," in which we've had 16 minor quakes (the biggest was a Magnitude 3.3) in the past month and 120 in the past year.
The loss of the rubber duckie was tragic to the point that there was an official “moment of silence” to mark the event. But the timing was also noteworthy on my side of the ocean because it came within a couple of weeks after many folks in southern Idaho reported feeling the shake of a Magnitude 3.6 temblor in the foothills near Victor, followed by two aftershocks in fairly quick succession. That was on Oct. 18.
And that naturally got some of the folks who have been here much longer than me talking about the Borah Peak Quake of Oct. 28, 1983, in which two children were killed by falling debris. Now regarded as the second most powerful quake along the North American Plate in recorded history, it was initially registered at a Magnitude 6.3, but has since been studied further and is now calculated as a Magnitude 7.3, followed in the next 10 months by at least 20 aftershocks of Magnitude 4.4 or more. Although the epicenter was in a sparsely populated area, it was enough to rip a trench in the earth, send rockslides tumbling, and displace the nearby ridges along the fault line by as much as 3 meters (9 feet). Landslides, rockfall and shaking strong enough to rattle buildings were commonly reported and recorded in a 1,600-mile radius of the epicenter.
Perhaps more significant was the disruption of the underground water table, more correctly the “hydrologic systems” in the nearby Salmon River, Thousand Springs Valley, and even the springs and geysers of Yellowstone National Park, powerful enough to alter the cycle of Old Faithful. In the area closest to the epicenter, ground water levels rose as much as 13 feet in a well, then subsided at a post-quake level about 5 feet above pre-quake levels. At Chilly Buttes on the day of the earthquake, seismic shaking produced a flow of groundwater from fractures in the limestone buttes that flooded the valley, and water levels in the underground Clayton Silver Mine rose enough to halt mining operations until pumps could be brought in to handle the increased post-quake flow.
South of Challis, at Ingram’s Warm Spring Creek, the quake had an opposite effect, drying up the spring and leaving hundreds of fish flapping to their death in the newly dry creek bed. Eight days later, however, the spring started flowing again, but much stronger, to the point that 46 days later, the flow rate was nine times its pre-quake level. The Salmon River and other streams draining the quake-affected area also flowed at much higher volumes for several months.
All this is a reminder that Idaho, despite outward sturdiness, is actually the fifth most seismically active state in the 48 contiguous states. And, as most of us folks with some time in Japan are aware, “seismically active” also means volcanically active. This should not be surprising, given that the state, while most famous for its potatoes, sugar beets, and a gold rush that out-yielded that of California, is sitting above one of Earth’s hottest hot spots. All around the Pacific Ocean, and extending to just a few blocks from my apartment, we find these areas in which the intense heat of earth’s core is transferred to the surface. One of the most noteable examples of this volcanic presence is not far northeast of Boise near Arco, at the Craters of the Moon National monument and Preserve, a convergence of three major lava fields along the Great Rift of Idaho, encompassing nearly 3,000 square kilometers (1,117 square miles) of high desert and sagebrush, including the deepest known open rift crack in the world – 800 feet deep – among many other impressive volcanic features that are the result of more than 25 distinct volcanoes, of which the most recent were within the past 2,100 years, and are recounted in native Shoshone legends that tell of a serpent on a mountain who, angered by lightning, wrapped himself around the mountain and squeezed it until the rock turned to liquid, fire shot into the air and the mountain exploded.

The lunar-like landscape in Idaho. From a trip we made in 2011 to Craters of the Moon.

For now in my neighborhood, this translates to the ability to have thermally generated heat in Boise’s midtown and at the Boise State University campus across the river. But this heat migration also melts rock, which is what makes volcanoes. Idaho also sits on the western edge of the North American Tectonic Plate, which converges with the oceanic plate that is somewhat west of us, beneath Seattle. When these plates grind against each other, and past another oceanic plate that intrudes into the southern part of the state – over the hot spot at Yellowstone across the border in Wyoming, we get earthquakes that are the result of both tectonism and volcanism. And we get some warm sidewalks.