Yellowstone's Deep Roots
Geophysics![Figure][1] 

CREDIT: THINKSTOCK

Yellowstone National Park in the western United States, renowned for its geothermal features, including geysers and hot springs, rests on a ∼4000-km2 caldera attributed to a series of supervolcano eruptions over the past 2 million years. The volcanic and geothermal activity is caused by the presence of a hot spot currently resting below the park that migrated eastward over the course of millions of years. Conflicting geological evidence implies that the source of this hotspot volcanism is either a deep plume originating hundreds of km below Earth's surface in the lower mantle or more shallow upper mantle melting caused primarily by extension of the continental lithosphere—a process that occurs elsewhere in the western United States. Schmandt et al. , analyzing data collected by the dense USArray seismic network while it was deployed across the region, addressed this debate through seismic imaging of the mantle below Yellowstone. Comparing the temperature-sensitive depth variation of mantle discontinuities at 410 and 660 km to global averages indicates the presence of a high-temperature upwelling that is vertically heterogeneous. The shallowing of the 660-km discontinuity, which marks the boundary between the upper and lower mantle, suggests that this plume-like structure originates in the lower mantle, but just how deep down remains unclear.

Earth Planet. Sci. Lett. 10.1016/j.epsl.2012.03.025 (2012).

 [1]: pending:yes