YELLOWSTONE VOLCANO OBSERVATORY MONTHLY UPDATE
Monday, February 2, 2009 10:52 MST (Monday, February 2, 2009 17:52 UTC)

YELLOWSTONE VOLCANO (CAVW#1205-01-)
44.43°N 110.67°W, Summit Elevation 9203 ft (2805 m)
Volcano Alert Level: NORMAL
Aviation Color Code: GREEN

Seismicity Summary: Beginning Dec 26, 2008, the second largest earthquake swarm of Yellowstone's recorded seismic history occurred beneath the north end of Yellowstone Lake. The swarm continued into Jan. 2009, but subsided rather quickly in activity on January 5. The Lake swarm consisted of 813 well-located earthquakes with magnitudes ranging from -0.8 to 3.9. This sequence contained 19 earthquakes of M>3.0 as well as 141 events of 2<M<2.9. Several of the M>3 swarm events were felt throughout Yellowstone National Park and surrounding area. For the entire month of January, 2009 315 earthquakes were located with 205 of these events associated with the Yellowstone Lake swarm, the largest being M 3.5 on January 2 at 11:32 AM MST. There have not been any reports of damage from the Yellowstone Lake swarm. Note that the largest earthquake swarm recorded in Yellowstone began in the autumn of 1985 on the west side of the caldera and east of West Yellowstone MT. It lasted for ~4 months and contained earthquakes of M>4.

In Jan. 9 to Jan 12, a secondary swarm of 35 earthquakes occurred near the northeast edge of the Yellowstone caldera, about 10 miles (16 km) NNE of the north end of the Yellowstone Lake swarm. This sequence included events with magnitudes of 0.4 to 3.3.

For comparison, Yellowstone commonly experiences 1,000 to 3,000 earthquakes per year and there have been more than 32,000 well-recorded earthquakes in Yellowstone from 1973 to 2009. Earthquakes that are closely spaced in time and area are termed swarms and are a common mode of seismic energy release in the Yellowstone caldera. From 1984 to 2008 there were 80 swarms documented in Yellowstone.

Earthquake activity in the Yellowstone was elevated during the Yellowstone Lake swarm but has returned to relatively normal background levels.

Yellowstone Volcano Observatory partners continue to analyze the seismic and ground deformation data from the Yellowstone Lake swarm and are evaluating any changes to the thermal areas located near the epicenters. If any changes are to be verified, they are quite small.

Ground Deformation Summary: Through January 2009, continuous GPS data show that much of the Yellowstone caldera continued moving upward, though at a lower rate than the past several years. The nearest GPS station to the swarm, at Lake Jct., about 2 km from the swarm has experienced ground uplift over the past 55 months of about ~18 cm (A plot of the vertical and horizontal ground motions at the Lake GPS station can be found at: http://pboweb.unavco.org/shared/scripts/stations/?checkkey=LKWY&sec=timeseries_plots&timeseries=raw). The WLWY station has undergone ~21 cm of uplift over the same time period. These and all other Yellowstone GPS data are being analyzed for unusual properties that may be associated with the Yellowstone Lake swarm. The general uplift of the Yellowstone caldera is of scientific importance and will continue to be monitored closely by YVO staff.

An article on the current uplift episode at Yellowstone and discussion of long-term ground deformation at Yellowstone and elsewhere can be found at: http://volcanoes.usgs.gov/yvo/publications/2007/upsanddowns.php.


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The Yellowstone Volcano Observatory (YVO) is a partnership of the U.S. Geological Survey (USGS), Yellowstone National Park, and University of Utah to strengthen the long-term monitoring of volcanic and earthquake unrest in the Yellowstone National Park region. Yellowstone is the site of the largest and most diverse collection of natural thermal features in the world and the first National Park. YVO is one of the five USGS Volcano Observatories that monitor volcanoes within the United States for science and public safety.