GEOL 3050

GEOL 3050 – Midterm Exam – Fall 2019
Due: Thursday, October 31 at the start of class, uploaded to Canvas.
Goal: On May 18, 1980, Mt. St. Helens had a violent eruption that removed a significant volume from the
volcano. This eruption killed 57 people and resulted in over $1,000,000,000 in property damage. Your
task is to complete a GIS analysis of the volcano before and after this event.
Rules: This is to be an entirely independent exam and you are banned from working on any parts of it with
your classmates. Please ask me if you have questions about the assignment and I will clarify.
Turn in: All things that need to be turned in are in bold. This includes two full-page proper map layouts
and a full-page view from ArcScene as well as answers to the questions. Compile this into a single
Word/PDF document and turn in to Canvas. Include proper units when reporting numbers and show your
work.
Datasets: You will be using the following provided data for your analysis (in the Exam folder on our
geode website):
• Hbefore (GRID file)
o This DEM is in a WGS84 geographic projection, but the file has been corrupted. You
will have to define this for ArcGIS to display properly.
• Hafter (GRID file)
o This DEM is in a NAD27 UTM Zone 10N projection, but the file has been corrupted.
You will have to define this for ArcGIS.
• Lidar_hlsd (GRID file)
o This is a high resolution hillshade of the present topography for use in your map and
ArcScene layouts. It may look funny when you load it, but this is just a symbology
problem (apply a stretch with a black to white colorbar).
• Points.shp (shapefile)
o This file includes two points for analysis in Step 6.
Tasks:
Step 1) Define the projections.
Step 2) Put all datasets into the NAD27 UTM Zone 10N projection so that your analysis will be accurate.
Be aware that projecting data will be slightly different for raster vs shapefiles (vector) data!”
Step 3) Make a proper layout showing gain or loss of elevation after the eruption. Use three classes:
one color showing loss, one transparent showing no change, and one showing gain of elevation. Use
the lidar hillshade as your basemap on the layout.
1) What is the maximum loss of elevation in the map area?
2) Where does this maximum loss occur? (include a latitude/longitude in decimal degrees and also a
description; e.g., on the southwestern flank of the volcano)
3) How did you make your elevation loss/gain raster? Write out a workflow of the steps you took in
ArcGIS to get to this point (starting at the beginning).
Step 4) Reclassify your elevation loss/gain map so that only areas that lost elevation are depicted.
Step 5) Make a south-looking ArcScene 3-D rendering of the post-eruption state that includes the
magnitude of lost elevation across the map. Use the lidar hillshade as your basemap. Classify your
lost elevation data in 100 m increments so one can assess the magnitude across your map area.
Export a nice south-looking oblique view of the volcano and include a legend if needed. Note for
the legend, you’ll have to make it in ArcMap and export/copy it for pasting onto the 3-D rendering.
4) What is the total 2-D area (in km2) that experienced elevation loss across the map region?
5) What is the total volume (in km3) lost across the map region?
6) Write out a workflow of the steps you took to determine the volume lost in the map area.
Step 6) Add the point1.shp and point2.shp files to your ArcMap project, which each only contain a single
point. Let’s say you had the unfortunate luck to be near Mt. St. Helens when it erupted. Your location
was at one of these two points. Analyze the loss/gain elevation data within a 300-meter radius of these
two points. This is about how far you might be able to run as the eruption started, to find a safe place to
ride it out.
7) What are the maximum, minimum, and average changes in elevation around each of these two
points? Construct a table to show your results.
8) Which of the two points would have been the safest during the 1980 eruption? Justify your
answer based on your GIS analysis.
9) Now have a look at the fairly accurate Wikipedia article on the 1980 eruption.
https://en.wikipedia.org/wiki/1980_eruption_of_Mount_St._Helens After reading about the various
local hazards, would either of these two points been safe during the eruption? If not, state what
would have likely killed you at your favored point.
10) Make a final full-page, landscape layout with two data frames: One showing the pre-eruption
topography of Mt. St. Helens and the other showing the post-eruption topography. For the preeruption view, use a hillshade and elevation colors from the hbefore DEM. For the post-eruption
view use the hafter DEM with a hillshade as the basemap. Include the same range/symbology of
elevation colors on both maps. Add 100 m contour intervals to both maps and label the elevations
of the contours (or include in your legend). On the post-eruption layout, also include a
representation of the blast zone of tree-removal.
11) Final Question: What was the summit elevation of Mt. St. Helens before and after the
eruption?

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