A plume of magma may explain North America’s odd geology
Earth’s active geologic processes are a blessing and a curse. They help sustain life. Yet, the last sign I saw as I entered the Washington State Fair this summer pointed to an evacuation route in the event of volcanic eruption. It is no secret most destructive events occur at plate boundaries. Earth’s crust consists of dozens of tectonic plates moving against one another, causing earthquakes and volcanoes. But these hazards are much less frequent in the middle of tectonic plates. In Iowa and the Amazon, you worry more about erosion, not volcanoes.
There are exceptions to this rule, and those exceptions are often caused by hotspots. Hotspots are regions of volcanic or earthquake activity caused by superheated plumes of magma that rise up from Earth’s mantle. These plumes melt rock and sometimes pierce the surface, triggering earthquakes and volcanoes. As a plate moves across a stationary plume, the plume can leave a train of volcanoes in its wake. The most famous example of these pock-marked scars is the Hawaiian Islands. The hotspot that created them has punched holes through the Pacific Ocean’s thin oceanic crust since dinosaurs roamed the Earth.
Unlike oceanic crust, continental crust is much thicker, posing a challenge for hotspots that want to be heard. The particularly violent hotspot beneath Yellowstone National Park has managed to breach thick continental crust several times. In its last major eruption 640,000 years ago, volcanic debris fell in Mississippi over 1,300 miles away. But Yellowstone is the exception, not the rule; geologists still struggle to understand just how hotspots behave beneath thick continental crust. In a paper published last week in Nature Geoscience, a team from the California Institute of Technology report evidence that eastern North America recently passed over a hotspot, with surprising implications for the continent’s geologic history. Continue reading