GEOSCI 106 Lab 5_ Volcanoes-March

GEOSCI/ENVIR ST 106: Environmental Geology Lab 5: Volcanoes Assignment overview: One of the major impacts of plate tectonics on human life is in the form of volcanic activity. Geologists collect a variety of data about volcanoes to understand future risks. In this lab, you will use data from maps and conduct some simple computations to explore volcanic hazards. Instructions: 1. Download the “Pacific NW volcanism.kmz” dataset associated with this lab in Canvas. 2. If you do not have Google Earth Pro, download and install it. It is freely available here: https://www.google.com/earth/versions/ . Note that the version of Google Earth in a browser will not suffice; you will need to use some functions that are only available in Google Earth Pro. 3. Fill out each red highlighted field (_________) according to each question’s instructions. Submission: To submit the assignment on Canvas, use the following steps: 1. In Google Docs, generate a PDF: File → Download as → PDF Document 2. In Google Docs, use Share → Get Shareable Link, and copy the link address 3. In Canvas, upload your PDF to the assignment. 4. In Canvas, paste the link address to your Google Doc in the assignment comments. Unit conversions: In this lab, you will need to convert imperial units to metric on a few occasions. Here are some unit conversions that you may find helpful. 1 foot = 0.3048 m 1 mile = 5280 feet = 1.609 km 1 km = 1000 m 1 km 3 = 10 9 m 3 1

Volcanic eruptions: Mt. St. Helens (1980) In Canvas, open the Google Earth file “Pacific NW volcanism.kmz”, and zoom in to Mt. St. Helens. You should see an image of a rectangular topographic map overlain on the satellite imagery. (If you do not see this, go to the Places window in Google Earth, click on the “Pacific NW volcanism.kmz” file, and make sure that the “Mt St. Helens, WA, 1:62,500 quad, 1958” is checked.) This is a topographic map from 1958, which shows the topography of Mt. St. Helens a couple decades before the 1980 eruption. Because this map is rather old, the elevation data it reports are in units of feet. By exploring the terrain in Google Earth, you should see that Mt. St. Helens juts up sharply against the surrounding topography. Here you will use this data to explore the topography of the volcano before it erupted. The first step is to orient yourself on the topographic map. If you have not looked at a topo map before, the following tips may help you interpret what you see: ● The thin reddish brown lines circling the volcano are contour lines. Each contour line connects locations with the same elevation. ● Some of the contour lines are a little thicker than the others. These are labeled with numbers that indicate the elevation of the contour line in units of feet. ● The rest of the contour lines are a little thinner and are not labeled. These indicate equally spaced elevation intervals between the thicker contour lines. 1. Topographic contour lines. What is the elevation difference between neighboring thin contour lines? This is known as the map’s contour interval. (Tip: Count the number of lines between two thick contour lines.) Report this in both feet (as the map shows it) and in meters. (1 point) 40_________ feet 12.192_________ meters 2. Estimating volcano slope. Using the line tool in Google Earth, draw a line from the pre-eruption peak of Mt. St. Helens (i.e., as indicated in the 1958 contour map) to the north, until you reach the 4,400-foot contour line on the map. What is the average slope of the volcano along this line? (Hint: Slope = elevation change in meters / lateral distance in meters.) (1 point) _0.356________ 3. Estimating pre-eruption volcano volume. By examining the topographic map, you may notice that the volcano before the eruption was roughly shaped like a cone. Here you will estimate the volume of the 2

_1/100________ (c) Use a density of 2700 kg/m 3 (typical of andesite) to calculate the mass of rock (in kg) that was blown off the volcano during the eruption. (1 point) 9.55x10^11kg_________ 5. Impact of the eruption. The Seattle metropolitan area is roughly 220 km 2 . If all of the rock erupted from Mt. St. Helens (as calculated in the previous question) had landed on Seattle, how thick would that layer be, in meters? (Hint: Dividing the volume of rock by the area over which it fell will give you a depth. Remember to convert this to meters!) (1 point) _1607m________ Highway 504, North of Mt. St. Helens, post-eruption. (USGS) 4

6. Shield volcano vs. stratovolcano topography. Hawaii’s Big Island has the largest volcanoes in the United States. Unlike Mt. St. Helens and the other stratovolcanoes in the Cascades, these are shield volcanoes. Shield volcanoes are built from lavas that flow more easily (i.e., they are less viscous) than the lavas that build stratovolcanoes, and as a result shield volcanoes tend to have gentler, broader slopes than stratovolcanoes. The largest volcano on the Big Island is Mauna Loa. In the Google Earth file, click on “Mauna Loa transect” to navigate to the Big Island. Here, the red line indicates a transect from one side of Mauna Loa to the other. This is composed of two straight lines, one from Point A to the summit (Point B), and one from the summit down the other side to Point C, each roughly aligned with the path of steepest descent. There are twenty placemarks along the transect, indicating the points at which you will need to measure distances and elevations, which you will need to report in Table 1. The first row represents Point A, and has already been filled out as an example. With the Ruler tool, measure the horizontal distance along the transect from Point A to each point on the transect. Because these must be distances along the transect, points on the opposite side of the summit from Point A (points 12-20) should be measured as the distance from Point A to Point B plus the distance from Point B to the point in question. Report these distances in the Distance column in Table 1. In the Elevation column of Table 1, record the elevation of each point. In Google Earth, you can find the elevation of the terrain under your cursor near the bottom right corner of the Google Earth window, where the cursor’s latitude, longitude, and elevation are shown. (3 points) 5

7. Mt. St. Helens transect. In the Google Earth file, go to the “Mt. St. Helens transect”. Like the Mauna Loa transect, this consists of a transect line and 20 placemarks. Fill out Table 2 with the distance of each point along the transect and its elevation, the same way you filled out Table 1. (3 points) Table 2. Mt. St. Helens transect Site Distance along transect (km) Elevation (m) 1 (Point A) 0 1067 2 618 1080 3 1393 1110 4 2129 1135 5 2952 1177 6 3880 1341 7 4483 1552 8 5122 1622 9 5885 1762 10 6504 1900 11 7276 2103 12 8031 2407 13 8521 2249 14 9167 1978 15 9815 1762 16 10544 1409 17 11275 1253 18 12117 1158 19 12893 1145 20 (Point B) 13809 1037 7

8. Plot elevation profiles. (a) Create an x-y plot with the elevation profiles for both the Mauna Loa and the Mt. St. Helens transects on the same plot, and paste the plot in the designated space below. Make sure both transects are on the same plot and that the plot has the following elements: X-axis showing distance from Point A, with an extent of 0 to 65 km Y-axis showing elevation, with an extent of 0 to 5000 m Labels on x-axis “Distance (km)” and y-axis “Elevation (m)” Labels for each profile with the volcano names You are welcome to use whatever software you like to generate this plot. If you choose to do this in Google Sheets (which you may find convenient because it is easy to copy a plot from Google Sheets into this Google Doc), you may find it easiest to follow these steps. 1. Open a Google Sheet from this Google Doc by going to File > New > Spreadsheet. 2. Copy the Distance and Elevation data from the Mauna Loa table (Table 1) and paste them into the first two columns of your Google Sheet. This data should be in rows 1-20 of columns A-B. 3. Copy the Distance and Elevation data from the Mt. St. Helens table (Table 2), and, starting at the row below your Mauna Loa data, paste them into columns A and B. This data should be in rows 21-40 of columns A-B. 4. Move the Mt. St. Helens elevation data one column to the right (i.e., from column B to C). The spreadsheet should now consist of 40 values in column A, 20 values in rows 1-20 of column B (and nothing below that in column B), and 20 values in rows 21-40 of column C. 5. Highlight columns A, B, and C and go to Insert > Chart. At the right side of the Google Sheets, under Setup, change Chart Type to Line Chart. This will generate an x-y plot with both elevation profiles. Paste your completed graph here. (3 points) 8

_The eruptions fully impacted the lake. This caused toxic gases to seep up and into the water. This led to the water being devoid of oxygen.________ 10