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Sloshing Detected in Yellowstone Lake Helps to Locate Magma Storage Region (2013)

Several years ago, using sensitive new monitoring equipment located in shallow boreholes, scientific staff from UNAVCO, a member institution of the Yellowstone Volcano Observatory (YVO), detected an odd rhythmic signal near Yellowstone Lake.

Map of area within Yellowstone National Park showing Yellowstone
Map is Figure 1 from Lutrell et al., 2013, showing the location of the borehole strainmeters (yellow hexagons), the stream gage (SG), weather station (KP60), and pressure gauge (APG) in Yellowstone National Park.

Further work demonstrated that this strain signal, with a 78-minute frequency, came from an intermittent seiche (pronounced "say-sh"), or standing wave, only an inch or two tall, within Yellowstone Lake (Plots below show seiche signal). These waves can be triggered by atmospheric phenomena such as high winds or barometric changes, and usually takes a few days to die off.

Fluid dynamic models show that the frequencies of the standing waves relate directly to the shape of the Lake (see "What is a Seiche?" at right). Multiple separate waves are present, representing oscillations in water flow among the multiple lake basins. Most surprising to the geophysicists was that the signal of these small waves along the lake's surface could be recognized 30 km (19 mi) away from the lake at a distant strainmeter (instrument locations in map above).

The strongest Yellowstone Lake seiche wave (primary mode) has a 78-minute period, but other weaker seiche waves are also present simultaneously.

USGS postdoctoral fellow Karen Luttrell, together with colleagues from UNAVCO and elsewhere, recently published an article in Geophysical Research Letters revealing how the presence of magma beneath the ground at Yellowstone allows the seiche signal to travel further than it would in the earth's crust under normal (magma-free) conditions (cartoon below illustrates amplification of seiche signal). In essence, instead of behaving like a solid (elastic behavior) like most of Earth's crust, regions beneath Yellowstone can slowly flow (viscoelastic behavior) and transfer strain across greater distance. The authors estimate that magma is present starting at 3—6 km (2—4 mi) beneath the ground surface, and that the magma is mostly crystallized but is still partly molten. The new results are consistent with and complementary to results from seismic and other studies (Smith et al., 2009) . YVO scientists continue to monitor the Yellowstone volcano area for any signs of unrest.

Data from three different instruments show the initiation of a stan...
Observations of a Yellowstone Lake seiche that began on 12 July 2012, apparently initiated by passing of a barometric high associated with high winds. Seiche is directly observed by an Absolute Pressure Gauge (APG) in the lake (top), and subtle ground motion from the seiche is observed by Borehole Strainmeter instruments at nearby Grant Village (middle) and distant Canyon Village (bottom). The strong 78-minute seiche signal begins during a passing weather front. (The signal with 12-hour period is from the always-present solid earth tide).
Cartoon cross-section through Yellowstone Caldera showing how the m...
Cartoon cross-section through Yellowstone Caldera showing how the magma beneath the surface makes the Yellowstone Lake seiche detectable very far from lake. (click for larger image)

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