Volcanic hazards: case histories, prediction of eruptions, and hazard maps
Lecture outline for environmental geology course
Figure of Mt. St. Helens looking to the east and taken in 1996. The red arrow shows the northward direction of the lateral blast, while the Tuttle River valley is show with the lahar deposits in the foreground. This is the edge of the blast zone, and dead trees litter the slopes in the lower left corner.
Mt. St. Helens: the classic example for the U.S.. May 18th, 1980
Mt. St. Helens in 2018 looking to the south from the hert of the main blast zone. One can see the lava dome that has built up in the depression left by the explosive 1980 eruption, along with the flanking glaciers. In the foreground soil is developing as a plant cover establishes itself in what was a totally barren landscape. One research stream in the area is how does life reinhabit such a 'sterilized' blast zone.
Krakatoa (Krakatau): a big one (but not the biggest). August 22nd, 1881, dormant for 200 years.
Mount Pelee - Martinique, West Indies, 1902
Nevado del Ruiz, Nov. 13 1985
Images and information from the 2018 Hawaiian eruptions - https://volcanoes.usgs.gov/volcanoes/kilauea/multimedia_videos.html .
Dante's Peak was a movie!
Possible precursors can monitor:
USGS graph showing the relationship between seismic activity (y axis) versus time (x axis) for the 1980s. The green arrows mark eruptions including the large initial eruption in 1980 that was described and discussed above. The red line is cumulative earthquake count, the sudden steps in which represent a marked increase in seismicity. Note that eruptions are often associated with a building intensity of earthquakes. Graph source: From Pacific Northwest Seismic Network https://pnsn.org/volcanoes/mount-st-helens#seismicity (accessed 11/12/18) .
This map is from an area in Oregon known as the Three Sisters, which has volcanically active in recent geologic times. The Three Sisters are volcanoes, and these are associated with Cascade volcanic arc in the Pacific Northwest that is in turn related to subduction off the coast. The colors represent the amount of vertical change in elevation seen when comparing satellite radar data from two different points in time (interferometry), and the lower layer shows the amount of uplift in units of millimeters in between 1995 and 2001. This is thought to be due to magmatic inflation, and thus the local volcanic risk is higher. There were not subsequent eruptions, which simply means the magma did not reach the surface (yet). Image is from USGS site: InSAR—Satellite-based technique captures overall deformation "picture" at https://volcanoes.usgs.gov/vhp/insar.htm
History of predictions:
Can an eruption be controlled or prevented?
So what's the concern? What specifically should be included in a hazard map for a volcanic region?
Image from USGS/CVO volcanic hazard program that nicely summarizes events and concerns possibly associated with an eruption.
Diagram from the USGS, who has primary responsibility for monitoring volcanoes in the U.S., of the various possible precursor phenomena that can be monitored to predict eruptions. Image source: https://volcanoes.usgs.gov/vhp/monitoring.html (accessed 11/12/18).
USGS volcanic eruption alert/warning levels (from https://volcanoes.usgs.gov/vhp/about_alerts.html (accessed 11/12/18)):
These alert levels are often consecutively assigned the following colors: green, yellow, orange and red. Other countries have similar, but somewhat different alert levels.
In class laboratory. Assessing Mount Hood.
Volcanos on the web. A lot of good case histories here.