The Sour Creek Dome This unassuming hill is found within Yellowstone National Park and is an important part of the story of the volcanic system that lies beneath.
Yellowstone National Park surrounds the Yellowstone Caldera, the remnants of a giant volcano that has produced 3 huge eruptions in the last 2 million years. The most recent of those eruptions occurred about 640,000 years ago; during that eruption a huge amount of molten rock fragments poured out of a magma chamber in the crust. This was the third major eruption on this site, so the process that governs these eruptions must be one that repeats. This small hill is part of that process. This is the Sour Creek dome, a piece of the caldera that pushed back up after the last eruption. The really big eruptions empty large spaces within the magma chamber below and the rocks above fall down into the hole, sinking like pistons moving downward on giant faults. The forces that drive huge eruptions don’t stop just because the pressure is released from the magma chamber. Only a small fraction of the magma below the volcano ever comes up to the surface; once the pressure is released, the magma chamber starts rebuilding itself. The pressure in the magma chamber begins to rise again after the major eruption as new molten rock and more heat arrives in the system. As this pressure increases, the rocks that slid down as a piston suddenly are pushed back up. This dome sits just to the north of Yellowstone Lake and when it moves, it actually causes the lake to shift slightly in response. The sour creek dome is a resurgent dome, one of two within the giant Yellowstone system. These resurgent domes are commonly found within caldera systems and all form by that same basic mechanism; a piston being pushed back up after the eruption ends. Since we’ve never actually watched one of these eruptions its uncertain how long it takes the system to push the piston back upwards; it could be centuries, millennia, or even longer. The entire floor of the Yellowstone system is active. As magma moves from one part of the region to another, some areas rise and some fall. This structure has existed for hundreds of thousands of years, long enough for its edges to erode. Since every time we write about Yellowstone we also get questions about what it means for future eruptions – basically it just means that Yellowstone is like any other caldera system in the world. Even movement up or down doesn’t signal that anything major is likely to happen any time soon. In fact, Yellowstone commonly sees small eruptions including lava flows or small hydrothermal explosions as magma moves around beneath the surface, and as a consequence it is one of the best-monitored volcanic systems in the world. -JBB Image credit: NPS Read more: http://www.greateryellowstonescience.org/download_product/511/0