Name:
Investigating Volcanic Hazards
Objectives
• To understand the hazards associated with explosive volcanic eruptions
• Use satellite images to create hazard maps
• Use data from a past eruption to predict the potential hazard of another volcano
Laboratory Materials Needed
• Ruler
• Calculator
• Drawing compass
Pre-lab Assignment
Prior to lab, read textbook Chapter 4 Sections 4.3, 4.4 and 4.5 and the USGS Volcanic Hazards handout (http://pubs.usgs.gov/fs/fs002-97/fs002-97.pdf) and the “Using Satellite Images To Determine Size” document. NOTE: You must use this calculation method when answering questions in the lab exercise. Measure all pictures using centimeters.
Exercise 1: Investigating Mount St. Helens
Mount St. Helens is located in Washington, 98 miles south of Seattle. Mount St. Helens’ May 18, 1980 eruption is the deadliest, most destructive eruption in the recorded history of the lower 48 states. Earthquake activity began in mid-March and over 10,000 small earthquakes preceded the eruption. Magma rising through Mount St. Helens resulted in a 450 foot tall bulge on the northern flank. A 5.1 magnitude earthquake collapsed the bulge, creating a debris avalanche and releasing the pressure on the underlying magma. Following the reduction in pressure, gas and other volatiles bubbled out from the magma, culminating in the 300 mph lateral blast which wiped out the old growth forest. Ash was sent vertically through the air, reaching a height of 15 miles in 15 minutes. Fifty-seven people were killed during the eruption of Mount St. Helens, including one geologist.
1. Prior to eruption, Mount St. Helens was 9,677 feet tall and had a diameter of 55,000 feet. Calculate the average slope and the angle of the slope of Mount St. Helens. You must show your calculations. Remember: Slope = rise / run
Angle of the slope = tan-1 (slope) = degree of slope
Calculations:
Slope = _______________________ Angle of the slope = __________°
2. Based on your calculated slope and its eruptive history, what type of volcano is Mount St. Helens (select one)? Note: Shield volcanoes have gentle upper slopes around 5° and steeper lower slopes around 10°. Stratovolcanoes have steeper upper slopes around 30° and gentler lower slopes (6-10°). Cinder cones have slopes between 25 to 35°.
______ Shield ______ Stratovolcano (Composite) ______ Cinder Cone
3. Observe Figures 1 and 2 in Appendix C of the 1973 and the 1988 false-color Landsat images of Mount St. Helens. Red represents forest, while gray-blue represents ash, mudslides and mud-loaded rivers. Water is black and ice and snow are white.
a. Comparing these images, how many kilometers from the central crater were deforested by the blast? Figure 2 covers a north-south (top-to-bottom) distance of 48 km. Measure the distance from the crater to the edge of the blast zone north of Spirit Lake. The edge of the blast zone is marked in Figure 2. NOTE: Use the technique from the handout to do these calculations and make all of your measurements in centimeters. Show all of your calculations.
Distance = __________________km
4. Now compare the stream valleys before and after the eruption. Several of the streams in Figure 2 are now filled by gray material. How was this material deposited? Explain your answer. (Note: the pre-eruption peak of Mount St. Helens was snowcapped.)
5. The debris avalanche created by the collapsed bulge sent a landslide down the north side of Mount St. Helens. The landslide carried debris down the North Fork Toutle River and had an average depth of 150 feet! Compare the number of lakes in Figures 1 and 2. How did the new lakes form? Propose a hypothesis to explain how they formed.
6. Currently, a new dome is building within the collapsed crater of Mount St. Helens. What do you suspect the future holds for this volcano?
Exercise 2: Developing a Hazard Map for Mount Rainier
Now, let’s apply what we learned from the eruption of Mount St. Helens to Mount Rainier, another volcano in the Cascade Range. Mount Rainier is located 54 miles southeast of Seattle, Washington. It is covered by 26 glaciers and is the tallest mountain in the Cascade Range, with an elevation of 14,410 feet. Mount Rainier last erupted in 1854.
7. Figure 3 in Appendix C is a Landsat image of Mount Rainier and spans a distance of 68 kilometers from north to south (top-to-bottom).
a. How many kilometers are represented by one centimeter? Show all your work.
1centimeter = ___________________ kilometers
b. How many miles are represented by one centimeter? Show your work.
1 centimeter = _____________________ miles
8. Pyroclastic material was ejected out of the top of Mount St. Helens following the lateral blast. This material was blown at speeds of 50-80 mph and was found up to 8 kilometers away from the central crater.
a. Assuming an explosive eruption similar to Mount St. Helens, use your compass to draw a circle with a radius of 8 kilometers around the center of Mount Rainier (Figure 3). Label this circle “pyroclastic flows.”
b. Are there any nearby towns shown in Figure 3 that might be affected by pyroclastic ejecta? If there are, what are their names?
9. Geologists studying Mount Rainier have noted that past eruptions involved dome collapse like Mount St. Helens.
a. To assess the potential hazard associated with a Mount St. Helens-style lateral blast, use a compass and the number you determined in question 3a to draw a circle of appropriate size around Mount Rainier (Figure 3). Label this circle “lateral blast.”
b. Are there any nearby towns shown in Figure 3 that might be affected by a lateral blast? If there are, what are their names?
10. Figure 4 in Appendix C is a picture of Mount Rainier viewed from Tacoma. Based on your observations in the photo, what do you suspect is the number one volcanic hazard associated with living in the shadow of Mount Rainier? Explain your reasoning.
11. 5,000 year-old deposits of volcanic mud have been found as far away as Puget Sound.
a. Using your aerial photograph (Figure 3), what is the map distance in centimeters from Puget Sound to the center of Mount Rainier? Use a ruler to measure this distance.
Map distance = ____________ cm
b. How far is this distance in kilometers (ground distance)? NOTE: Use conversion factor from question 6. Show all your work.
Ground distance = ____________ km
c. How far is this distance in miles? Show all your work.
Ground distance = ____________ miles
d. Lahar deposits during the Mount St. Helens eruption traveled 50 miles down the Cowlitz River at speeds of 10-20 mph. Over 200 homes and 27 bridges were wiped out by the lahar.
i. How does the distance you calculated compare with the lahars created by Mount St. Helens in 1980? Be specific.
ii. Would the destruction caused by Mount Rainier be greater than, less than or about the same as that of Mount St. Helens? Consider both the ground distance from your calculations and near by populations when determining your answer. Explain your reasoning.
Exercise 3: Investigating Volcanoes with Google Earth
In this exercise, you will use Google Earth to investigate other notable volcanic areas. To begin, open Google Earth on your computer. Use the search box to explore the different volcanoes below. You will need to use the ruler tool in Google Earth to measure distances.
12. Search for Kalapana, Hawaii. Adjust the zoom to 13,000 feet. In 1986, a lava flow from Kilauea’s volcano destroyed and partially buried most of the town.
a. What is the width in kilometers of the flow from north to south?
b. Zoom into the area. Spend some time exploring the damage created by the flow. Are there any houses left in the area?
c. Fly to Kaimu-chain of Craters Road (make sure that the roads layer in Google Earth is on). Zoom in to an altitude of 2,000ft. What happened to this road?
13. Type 19°24’23.70″N, 155°16’58.73″W in the search box.
a. What is the name of this volcano?
b. Zoom in to an altitude of 7,000ft. What volcanic feature is shown in this area? (select one)
________ Crater ________ Caldera ________ Fissure ________ Parasitic Cone
c. What is the elevation in feet of the highest point of the rim?
d. What is the elevation in feet inside the volcano? (lowest point)
e. What is the height of the rim wall?
14. Search for Crater lake, Oregon.
a. What is the main volcanic feature in this area? (select one)
________ Crater ________ Caldera ________ Fissure ________ Parasitic Cone
b. What is the elevation of the lake?
c. What is the elevation in feet of the highest point of the rim?
d. What is the height of the rim wall?
e. What is the diameter of the lake from east to west?
15. Search for Mt. Shasta volcano.
a. What is the elevation in feet of the volcano?
b. Explore the west side of Mt. Shasta (~1.5 miles away from the volcano). What geological feature can be found in this area?
________ Crater ________ Caldera ________ Fissure ________ Parasitic Cone
16. Search for Mt. Vesuvius Volcano. This volcano was formed by the collision of the African and Eurasian plates. Geologic records indicate the oldest volcanic rocks are ~25,000 years old. During the most recent eruption in 1944, several villages were destroyed during this event. The most notorious eruption was in 79 A.D., during which the towns of Pompeii and Herculaneum were destroyed by pyroclastic flows and volcanic material. There are more than 3,000,000 people currently living near this volcano.
a. How many miles away are the closest villages?
b. What is the number one volcanic hazard in this area?