Friday Headlines, August 29, 2014
THE LATEST IN THE GEOSCIENCES
Shaking in Napa Valley
Iceland’s Volcano about to Blow
… Updated: It’s Erupting now.
The Mystery of Death Valley’s Racetrack Playa Rocks is Solved!
Geology of the Napa Valley Earthquake
On August 24th, a magnitude 6.0 earthquake struck near California’s famous Napa Valley, wreaking havoc in wineries, but fortunately taking no lives. This was the largest earthquake in California since the Loma Prieta quake in 1989 that preempted the World Series, and resulted in many many fatalities as bridges collapsed.
This earthquake – and all the quakes so common in California – are part of the greater San Andreas Fault system. These faults mark the boundary between two massive tectonic plates: the North American Plate, to the East, and the Pacific Plate to the West. The Pacific Plate is slowly sliding northward, relative to the rest of the continent, causing all the earthquakes.
…There’s the volcano in Iceland that’s fixing to blow. Bárðarbunga (BOWR-thar-Boon-kah, “Bárður’s Bulge”) is a volcano that’s been rumbling for a while now. While it seems relatively calm on the surface, geologists suspect that recent earthquake activity has been caused by magma moving below the surface, looking for a vent though which to escape.
In 2010, a different volcano, Eyjafjallajökull, erupted, causing a disruption of flights for six days. in the winter of 1783 to 1784, a massive Icelandic volcano called Laki (Eldgjá) went off for about 8 months, resulting in millions of deaths.
Could Bárðarbunga prove to be another Eyjafjallajökull? Or worse, another Laki ? I guess we’ll find out soon.
But why, you may ask, are there so many volcanoes on Iceland?
The answer is because Iceland lies along the Mid-Atlantic Ridge, a massive volcanic mountain range that lies beneath the waters of the Atlantic Ocean and spans the entire North-to-South length of the Ocean. Volcanoes along this ridge are slowing pressing Europe and Africa away from North and South America. The Mid-Atlantic Ridge is a spreading center.
It just happens that in Iceland, the peaks of the Mid-Atlantic Ridge rise above the ocean surface. This results in lots of visible volcanic activity.
UPDATE: Mere hours after publishing this post, Bárðarbunga began to erupt. Read more here.
Mystery of Death Valley’s Sliding Rocks Solved
For as long as I’ve been involved in this geology gig, the sliding rocks of Racetrack Playa have been a mystery.
“Runningrock2” by Tahoenathan – Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.
It appears that large boulders have slid across the barren and dry playa bed, leaving long trails behind them. But how could a boulder move like that?
Scientists long suspected that ice, plus heavy winds, were the culprit. Because such circumstances seemed likely to be inhospitable to humans, researchers from Scripps Institute of Oceanography implanted GPS units into several large stones on the playa and just left them to sit – and hopefully move.
What these scientists were surprized to find was that, while ice was important in the movement of the rocks, only a gentle breeze on a lovely crisp day was sufficient to do the work.
And they caught it on video: