Geology 210 – Lab #2 – Volcanic Hazards

Spring, 2003

Introduction:  This week’s lab will involve an examination of volcanic hazards in the Cascadia volcanic system; specifically we will compare and contrast the effects of the 1980 eruption of Mt. St. Helens with present-day hazards in the Mt. St. Helens and Mt. Rainier areas. In addition, we will use Surfer to examine a topographic data files of the Mt. St. Helen’s area and generate maps which depict the changes in the area that resulted from the eruption 

Before lab, please read and/or download the following .pdf files:

Mt. Rainier Hazards

Mt. St. Helens Hazards

These are located in the lab2 folder on the network..

Note that the .pdf files of the various maps that we will use in class are also available in that network folder, along with the DEM files that will be used in this lab.

You should also visit the websites listed below to gain additional background on the Cascadia volcanoes and volcanic hazards in that region.

http://www.usgs.gov/themes/volcano.html

USGS Volcano Homepage

http://vulcan.wr.usgs.gov/Publications/hazards_reports.html

Cascades Volcano hazards maps and pubs.

http://vulcan.wr.usgs.gov/Volcanoes/Rainier/Hazards/framework.html

Description of Mt. Rainier Hazards

Exercises:

1. Cascadia Volcanic System:

a. Briefly describe the plate tectonic origin of the Cascade Volcanic Arc.

b. What is the general composition (mineral and chemical) of the Mt. Rainier and Mt. St. Helens magmas and lavas?

c. How does the composition of these magmas and lavas influence the eruptive style of the volcanoes?

2.  Comparison of Mt. St. Helens 1980 eruption with hazards predicted for future eruptions of Mt. St. Helens and Mt. Rainier: Please refer to the hazards maps available in the lab room, and refer to the documents and websites listed above.

a.  Explain why the areas of the various hazards zones shown on the 1995 Mt. St. Helens hazards map are much less extensive than the actual areas affected by the 1980 eruption.

b. Why are the projected hazards for Mt. Rainier more extensive in aerial coverage than the 1995 Mt. St. Helens hazards map?

Mt. St. Helens Before and After:

In this exercise we will make use of .dem files (digital elevation files) of the Mt. St. Helens area that describe the topography of the area before and after the eruption.  .dem (stands for digital elevation model) files are grid files that use a UTM grid and have elevation as the “Z” variable.  They are available from the USGS and other sources and can be used for a variety of topographic analyses.

1.  Open Surfer and examine the two data files using Map-Contour Map option.  Note that one of the files is a .dem and the other a .grd – both have the same UTM grid coverage, and depict the pre and post-eruption topography. What are the N-S and E-W dimensions of the coverage? What is the spacing of the data points in the grid?

2.  Use the Grid-Math option to produce a new grid file which depicts the elevation change caused by the eruption.  You will want to do this such that the areas that lost elevation during the eruption produced negative values and the areas that gained elevation produce positive values.  Use the newly generated grid file to plot a contour map showing the distribution of areas that gained and lost elevation.  You may wish to use different colors and/or filled contours to illustrate this.  What processes were involved in the redistribution of materials that this map represents?

3. Use the Grid-Volume option to subtract one grid from the other and calculate the volume gain or loss across the area of coverage.  You will need to think carefully about what is subtracted from what, and the nature and meaning of the resultant data.   Explain your results.