Travel Reference
In-Depth Information
What does this heavy breathing and rumbling by the earth mean about possible eruptions?
While the inflation of the domes could be due to rising magma, it's hard to explain the de-
flation without an eruption of lava, and there hasn't been such an eruption in the last 72,000
years.
Geoscientists have not detected magma close to the surface. Most think the inflation and
deflation of the domes, as well as some of the mini-earthquakes, are due to movement of gases
and hot water at depth, not to movement of magma. Some of the small earthquakes that are
outside the caldera occur near the area of the large 1959 earthquake that formed Quake Lake
(see
page 36
).
For these reasons geoscientists think that an explosive event that spews large amounts of
tephra and forms another caldera is
not
likely in the near future.
While a large event involving hundreds of square miles is not of immediate concern, a
commonly recurring acute hazard is a hydrothermal explosion such as the one that formed
West humb Bay (see
pages 138-39
)
. Hydrothermal explosions are caused by hot subsurface
waters that flash to steam, breaking the overlying rocks that confine them and ejecting the
debris to form a crater. At least 26 such explosions have been documented in the more than
140-year historic record of Yellowstone National Park. Some have been preceded by no recog-
nized warning signs; thus, one purpose of the monitoring program at Yellowstone is to identi-
fy warning signs of such explosions. Progress is being made.
—B.J.G./J.S.
