Saturday, October 20, 2012

Quake Swarm In SW Yellowstone Caldera

A minor earthquake swarm of upwards of 30 events has occurred in Yellowstone National park, just SW of the rim of the caldera, and just inside the Island Park caldera. The events were at depths ranging from 20km-9km. This could indicate a small injection of magma into Yellowstone's upper magma chamber, but could also be nothing more than crustal adjustments.

Yellowstone's magmatic system is considered to be in two distinct parts. The first, deeper part is the actual mantle plume, which stretches to the NW into Montana (or rather far under it), with the second, shallower (3-5km deep) magma chamber that is actually responsible for the hydrothermal system being much shallower. Volcanogolgists consider the shallower magma chamber to be made of a 'crystal mush', or slightly cooler magma that is only partially molten. This chamber gives off plenty of heat, and is the cause of the geysers in the national park.

An injection of fresh magma into this chamber from the mantle plume would give some cause for concern, and would heighten the chance of an eruption, however probably not an eruption of massive proportion that most people fear from Yellowstone. Indeed, while Yellowstone is responsible for some of the world's largest eruptions in prehistoric times (the last 'super-eruption' being somewhere around 600,000 years bp), it can and does produce much smaller eruptions such as phreatic explosions.

It is likely that this is normal behavior for Yellowstone, as yearly, it produces plenty of volcanic earthquake swarms. If this was a magmatic intrusion of any kind, it will likely not manifest on the surface, as the magma chamber is literally humongous, and such a small amount of magma, if any, that is injected would be like a drop of water into a lake.

The quake swarm appears to only have lasted one day, and so far has not produced many aftershocks, which is what leads me to believe that this is probably at least a small dike intrusion, or some mantle plume activity (possibly an underground collapse at great depth). In any case, I'm always looking for a good excuse to write about Yellowstone, as it is a fascinating, beautiful, and potentially terrifying volcano. If anything further develops, you can be assured I will cover it!

Below is a picture of the current swarm from Google Earth/USGS.


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