The West Old & New Vol. III Issue III March 2014 | Page 13

(640,000 years ago).
The volcanic eruptions, as well as the continuing geothermal
activity, are a result of a great cove of magma located below
the caldera's surface. The magma in this cove contains gases
that are kept dissolved only by the immense pressure that the
magma is under. If the pressure is released to a sufficient degree by some geological shift, then some of the gases bubble
out and cause the magma to expand. This can cause a runaway
reaction. If the expansion results in further relief of pressure,
for example, by blowing crust material off the top of the
chamber, the result is a very large gas explosion.
According to the analysis of earthquake data in 2013, the
magma chamber is 80 km (50 mi) long and 20 km (12 mi)
wide, and is shaped like 4,000 km3 (960 cu mi) underground
mass, of which 6–8% is filled with molten rock.
Due to the volcanic and tectonic nature of the region, the Yellowstone Caldera experiences between 1000 and 2000 measurable earthquakes a year. Most are relatively minor, measuring a magnitude of 3 or weaker. Occasionally, numerous
earthquakes are detected in a relatively short period of time,
an event known as an earthquake swarm. In 1985, more than 3000 earthquakes were measured over several months. More than 70
smaller swarms have been detected between 1983 and 2008. The USGS states that these swarms could be caused more by slips on
pre-existing faults than by movements of magma or hydrothermal fluids.
In December 2008, continuing into January 2009, more than 500 quakes were detected under the northwest end of Yellowstone Lake over a seven day span, with the largest registering a magnitude of 3.9. The most recent swarm started in January 2010
after the Haiti earthquake and before the Chile earthquake. With 1620 small earthquakes between January 17, 2010 and February
1, 2010, this swarm was the second largest ever recorded in the Yellowstone Caldera. The largest of these shocks was a magnitude
3.8 on January 21, 2010 at 11:16 PM MST. This swarm reached the background levels by 21 February.
The last full-scale eruption of the Yellowstone Supervolcano, the Lava Creek eruption which happened nearly 640,000 years
ago, ejected approximately 240 cubic miles (1,000 km3) of rock, dust and volcanic ash into the sky.
Geologists are closely monitoring the rise and fall of the Yellowstone Plateau, which measures on average 0.6 inches (1.5 cm)
yearly, as an indication of changes in magma chamber pressure.
The upward movement of the Yellowstone caldera floor between 2004 and 2008 — almost 3 inches (7.6 cm) each year — was
more than three times greater than ever observed since such measurements began in 1923. From mid-summer 2004 through midsummer 2008, the land surface within the caldera moved upward as much as 8 inches (20 cm) at the White Lake GPS station. By
the end of 2009, the uplift had slowed significantly and appeared to have stopped. In January 2010, the USGS stated that "uplift of
the Yellowstone Caldera has slowed significantly" and that uplift continues but at a slower pace. The U.S. Geological Survey, University of Utah and National Park Service scientists with the Yellowstone Volcano Observatory maintain that they "see no evidence that another such cataclysmic eruption will occur at Yellowstone in the foreseeable future. Recurrence intervals of these
events are neither regular nor predictable." This conclusion was reiterated in December 2013 in the aftermath of the publication of
a study by University of Utah scientists finding that the "size of the magma body beneath Yellowstone is significantly larger than
had been thought."
Other media reports were more hyperbolic in their coverage.
A study published in GSA Today identified three fault zones that future eruptions are most likely to be centered on. Two of
those areas are associated with lava flows aged 174,000–70,000 years, and the third area is a focus of present-day seismicity.
Studies and analysis may indicate that the greater hazard comes from hydrothermal activity which occurs independently of
volcanic activity. Over 20 large craters have been produced in the past 14,000 years, resulting in such features as Mary Bay, Turbid Lake, and Indian Pond which was created in an eruption
about 1300 BC.
In a 2003 report, USGS researchers proposed that an
earthquake may have displaced more than 77 million cubic
feet (2,200,000 m3) (576,000,000 US gallons) of water in
Yellowstone Lake, creating colossal waves that unsealed a
capped geothermal system leading into the hydrothermal
explosion that formed Mary Bay.
Further research shows that earthquakes from great distances do reach and have effects upon the activities at Yellowstone, such as the 1992 7.3 magnitude Landers earthquake in California’s Mojave
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