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Eruptions of Mount St. Helens: Past, Present, and Future

In this project, you will visit a United States Geological Survey (USGS) website to learn about Mt. St.

Helens, one of the most active volcanoes in the United States. Read the pages on the website carefully

and answer the following questions. You do not need to write your answers in complete sentences.

Create a Word document with only your answers. You will upload your file to Canvas when completed.

There are 50 questions and each question has 2 parts, and each part is worth ½ point, for a total of 50

points for this lab. Due June 12 by midnight.

To begin, go to http://pubs.usgs.gov/gip/msh

Click on *Title Page*

From the Title Page, Click on *Contents*

From the Contents page, Click on *Preface*

Question 1.

a. What was the date (month, day, and year) of the climactic eruption?

a. Look at the photo caption. What was the maximum height of the ash and gas column from this eruption?

Question 2.

a. What kind of geologic activities preceded the climactic eruption?

b. Before the climactic eruption occurred, how long had the geologic activities you described above gone on?

At the bottom of the page, Click on *Introduction.*

Question 3.

a. Where is Mt St. Helens located?

b. What is the name of the mountain range that this volcano is in?

Question 4.

a. What kind of volcano is Mt St Helens? Give the 2 names for this kind of volcano that are listed on this page.

b. Describe what these kind of volcanoes look like and what they are made of.

Question 5.

a. Do stratovolcanoes typically erupt in an explosive or non-explosive manner?

b. Do the shield volcanoes of Hawaii typically erupt in an explosive or non-explosive manner?

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Click on *Cascade Range* next to the small map on this page to see a larger map showing the location of

the volcanoes of the Cascade Range.

Question 6. Count the volcanoes shown here.

a. How many volcanoes are there?

b. What 3 U.S. states include these volcanoes?

Close the map and return to the Introduction page.

Question 7.

a. What did the Native American Indian name for the volcano mean?

b. Who named the volcano Mt St Helens, and who was it named for?

Question 8.

a. Was there any evidence prior to the climactic eruption in 1980 that this was an active volcano?

b. Do scientists consider the volcanoes of the Cascade Range to be potentially dangerous?

Click on *Previous Eruptive History*

Question 9.

a. How old are the oldest ash deposits associated with ancestral Mt St Helens?

b. Scientists are aware of how many main pulses of volcanic activity prior to the 1980 activity?

Question 10.

a. Has Mt St Helens been continuously active for the last 10,000 years, or have periods of dormancy alternated with periods of activity?

b. Mt St Helen’s visible cone formed within the past how many years?

Question 11.

a. Prior to the 1980 eruption, was Mt St Helens heavily affected by erosion?

b. Were there any scientific predictions for the eruption?

Click on *Reawakening and Initial Activity* at the bottom of the page.

Question 12.

a. On what date did the first significant eruption of Mt St Helens occur?

b. Prior to that eruption, what peak in the Cascade Range had been the most recent to erupt?

Question 13.

a. What is “volcanic tremor?”

b. What does volcanic tremor reflect?

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Question 14.

a. Why did a bulge form on the volcano?

b. In April, when laser beams were used to measure the bulge, how fast (in feet per day) was it

growing?

Click on *The Climactic Eruption of May 18, 1980* at the bottom of the page.

Question 15.

a. Were there unusual changes in the volcano’s activity on the morning of May 18, 1980 that warned of the impending eruption?

b. Shortly after 8:32 am PDT, an earthquake occurred beneath the volcano. What did this do to the bulge on the north flank of the volcano?

Click on *Debris avalanche* at the bottom of the page.

Question 16.

a. The collapse of the north flank, triggered by the earthquake mentioned in the above question, produced a large landslide-debris avalanche. How fast did this avalanche move?

b. How many miles down the valley of the North Fork of the Toutle River did the avalanche travel?

Question 17.

a. How many square miles did the avalanche cover?

b. What was the average depth of the avalanche debris that filled the valley?

Click on *Lateral “blast”* at the bottom of the page.

Question 18.

a. When the north flank collapsed, the volcano was “uncorked.” What was the result of this “uncorking”?

b. What was the velocity at which the lateral blast traveled?

Question 19.

a. How far away from the mountain did the lateral blast cause devastation?

b. What was the average radius of the direct blast zone, in which virtually everything was obliterated or carried away?

Question 20.

a. Was this the first occurrence of a lateral blast in Mt St Helens’ history?

b. Which of these caused most of the casualties and destruction:

1. lateral blast, debris avalanche, and associated mud flows and floods

2. volcanic ash fallout downwind

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Click on *Ash eruption and fallout* at the bottom of the page.

Question 21.

a. Shortly after the lateral blast, a vertical explosion began. How long did it take the ash and steam column from the vertical explosion to reach an altitude of 12 miles?

b. What caused forest fires at this time?

Question 22.

a. In what direction did the major plume drift?

b. Why did the plume drift in this direction?

Question 23.

a. How fast did the ash cloud travel?

b. For how many hours did the eruption continue?

Question 24.

a. How long did it take for the ash to drift around the globe?

b. Examine the United States map shown here. According to the map, did any ash fall in Utah?

Question 25.

a. How many millions of tons of ash fell from the eruption?

b. What was the area, in square miles, that the ash fell over?

Question 26.

a. How large and deep was the new crater on Mt St Helens that resulted from the eruption?

b. How many vertical feet did the mountain lose during the eruption?

Click on *Pyroclastic flows* at the bottom of the page.

Question 27.

a. What are pyroclastic materials?

b. What is volcanic ash?

Question 28.

a. What is a pyroclastic flow?

b. What is the French term for a pyroclastic flow? What does it mean in English?

Question 29.

a. How fast can pyroclastic flows travel?

b. How many pyroclastic flows occurred during the May 18 eruption?

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Click on *Mudflows and floods* at the bottom of the page.

Question 30.

a. Where did the water come from that was in the Mt St Helens mudflows?

b. Geologists often use an Indonesian word to describe a mudflow on the slopes of a volcano. What is this term?

Question 31.

a. Looking at the map on this page, which one of these covered the greatest area?

1. the pyroclastic flow deposits

2. the mudflow deposits

3. the lateral blast zone

4. the debris avalanche deposits

b. From your study of this map, did the mudflows and debris avalanches pretty much follow the

course of the rivers in the area?

Question 32.

a. What was the speed of the mudflows once they reached the Toutle River drainage?

b. The “bathtub-ring” mud lines show that the height of the larger mudflows averaged how many feet deep?

Click on *The catastrophic first minute* at the bottom of the page.

Question 33.

a. Study the amazing photos at this site of the first minute of the eruption. What is the name of the person credited with having taken these photos?

b. About how many miles away from the summit was the photographer when he caught these images?

Click on *Impact and aftermath* at the bottom of the page.

Question 34.

a. How many lives were lost in the May 18, 1980 eruption of Mt St Helens?

b. How did most of the victims die?

Question 35.

a. How many houses and cabins were destroyed?

b. How many miles of roads were destroyed or damaged?

Question 36.

a. How many big game animals perished in the 1980 eruption?

b. Why did small animals like burrowing rodents, frogs, salamanders and crawfish survive the

eruption?

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Question 37.

a. How long was Interstate 90 closed between Seattle and Spokane after the eruption?

b. Name at least one of the indirect or intangible costs of the eruption.

Read through this section to the end, then click on *Comparisons with other eruptions* at the bottom of

the page.

Question 38.

a.What are the 2 most commonly used and directly measurable factors for standardizing the relative

sizes of volcanic eruptions?

b.List the 3 calderas in the U.S. that had gigantic pyroclastic eruptions in the geologic past.

Question 39.

a. What is the VEI?

b. On the VEI scale, what would be the rating of the 1980 Mt St Helens eruption?

Question 40.

a. Looking at the diagram showing Ejecta volume in cubic miles, what eruption is the largest shown?

b. When did it occur?

Question 41.

a. Looking at the table showing Volcanic Explosivity Index (VEI) of the deadliest eruptions since

A.D. 1500, which eruption (location and year) has the highest VEI?

b. How many casualties resulted?

Click on *Subsequent eruptive activity* at the bottom of the page.

Question 42.

a. What is a lava dome?

Be sure to click on *First lava dome* next to the photo to get an idea of the scale of the crater and lava

dome.

b. According to the last paragraph on this page, if the lava dome grows at its average rate of the 1980s, how long would it take to re-build the mountain to its pre-1980 eruption size?

Click on *Possible Future Behavior* at the bottom of the page.

Question 43.

a. What is the meaning of the term ‘eruptive period’?

b. Do scientists think that Mt St Helens may experience another explosive eruption with heavy ash fall before returning to a dormant state?

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Click on *Continuing Volcanic and Hydrologic Hazards* at the bottom of the page.

Question 44.

a. If a lava flow were to occur from Mt St Helens, is it expected to cause a great many deaths or a lot of destruction to property?

b. Name the 2 greatest hazards related to volcanic activity at Mt St Helens at the present time.

Question 45.

a. How could a devastating mudflow or flood be triggered?

b. During which season is the risk from mudflows and floods most significant?

Question 46.

a. What are some of the measures that have been taken by the USGS, the National Weather Service, and the Army Corps of Engineers to mitigate mudflow and flooding hazards?

b. Why was there concern about a possible breach or break of a natural dam located at South Fork Castle Creek?

Click on *Scientists’ challenge and opportunity* at the bottom of the page.

Question 47.

a. Why was the number of human deaths relatively low in the May 18, 1980 eruption?

b. Who is the Cascades Volcano Observatory (CVO) named for?

Question 48.

a. Where are the 2 ‘sister’ USGS volcano observatories located?

b. Have scientists been successful in providing warnings for eruptive episodes of Mt St Helens since the May 1980 eruption?

Click on *Mount St Helens National Volcanic Monument* at the bottom of the page.

Question 49.

a. Which U.S. President signed into law the measure that set aside the area around the volcano as the Mount St Helens Volcanic Monument?

b. How many acres does the Monument encompass?

Click on *Selected viewings and readings* at the bottom of the page.

Click on *Endnotes* at the bottom of the page.

Question 50.

a. What is the name of the lake shown in the top photo on this page? b. What is the common name given to the red flowering plant in the bottom photo, that was among

the first plant life to reappear after the 1980 eruption?

This is the conclusion of the Mt St Helens project. Be sure to submit your assignment online

through Assignments.