This week's lab assignment has three parts:

1. Volcano Hazards
2. Earthquake Hazards
3. Virtual Field Site Questions

Return to schedule

I. Volcanic Hazards

1. Name the four nearest active or dormant (potentially still active) volcanoes to your home.
2. How far away from your home is the nearest active or dormant (potentially still active) volcano?
   
   Notes on answering this question:
   
   
   • One item to be sure you include in your answer is where your home is -- which town and/or area of the state.
   • "How far away" is asking for a distance, not a time. Lava and ash do not drive on roads, so road maps on the Web may not provide an easy answer to this question. Apocryphal crows know the answer, because they fly in a straight line.
   • A volcano does not have to be erupting right now to be considered active, it just needs to have erupted during the Holocene epoch (during the last 10,000 years). (To pick a different definition of active, a volcano is considered historically active if it has erupted during historical times, since humans who write things down have been around. But then, this is a geology class, not a history class.)
     
     
3. How many years ago was the last time a volcanic eruption deposited volcanic ash in your neighborhood? Note: Ash from the 1980 Mt. St. Helens eruption did not reach everywhere in the Northwest. Ash from the much larger eruption that formed Crater Lake reached virtually all the Pacific Northwest.
4. Write a paragraph summarizing the potential for a volcanic eruption disrupting your home area. Take into account the nearest active volcanoes, the ways that any of them have affected your home area in the past, and the fact that prevailing winds in the Northwest tend to come from the west towards the east. State which type of eruption your home area is most at risk to-lava flows or ash falls. Composite cone volcanoes like Mt. Rainier erupt lava about ten times as often as they erupt ash, but the lava rarely flows more than 20 miles from the volcano.

You can find important information about active volcanoes in the Cascade Range, including where they are, in the Volcanoes section of the USGS Cascades Volcano Observatory website: http://vulcan.wr.usgs.gov/

II. Earthquake Hazards

5. Briefly describe the effect of the February, 2001 Nisqually earthquake (the one that shook Seattle a lot) on your home neighborhood. Did you feel it? Did it cause any rattling of things on shelves? Did it make people queasy? Did it cause any actual damage in or near your home neighborhood?

• Note: If you did not experience the 2001 Nisqually earthquake but have experienced some other earthquake, describe the earthquake experience that you did have, including when and where it was. If you have never felt an earthquake, describe some of the things that you have heard happens to people as they experience an earthquake.

6. Name the nearest active fault or zone of active faulting (zone of earthquake activity) to your home.
   
       Notes on active faults in Washington state:

• Spokane has either the recently active Latah Creek fault or else an unnamed active fault nearby.
• Seattle has the Seattle fault (also called the Seattle-Bremerton fault) which had a magnitude 5 earthquake in the mid-1990s and has had much larger earthquakes farther back in the Holocene epoch.
• The Entiat area has an unnamed active fault in north central Washington. This was the site of the great earthquake of 1872, which was one of the most powerful earthquakes to shock the Pacific Northwest in the last two centuries. Few people lived in the area at the time, so there was no loss of human life, and direct eyewitness accounts are lacking. The exact fault location has not yet been discovered.
• The Malott area in Okanogan County has an unnamed active fault.
• The Walla Walla area has the Hite fault and some other active faults nearby, which have produced noticeable earthquakes in the last century.
• Portland has the recently verified Portland Hills fault.
• Other active faults in the Puget Lowlands include the South Whidbey fault and other faults in northwestern Washington and the northern Olympic Peninsula.
  
• You should do some research on the Web to complete your solution to this problem. It also can help to bring it up and discuss it with other students.

7. Think of the state of Washington as having two levels of earthquake hazards. Level 1 is those parts of the state likely to be near enough to the centers of devastating earthquakes in the next century to be subject to damage to buildings. Level 2 is those parts of the state likely to be far enough from major earthquakes to not suffer significant damage to buildings, while still at risk for small to moderate earthquakes nearby. State which level you think your home area is, and give specific reasons why.
   
   Be sure you include the larger picture in your discussion of seismic (i.e. earthquake) hazards in your area. This includes:

• The larger picture in terms of geologic history. Your relatively short-lived memory, and that of your parents and grandparents, does not count for much in the geological scheme of things. You should consider what seismic activity there has been in your area in the last 10,000 years, or at least the last 1,000 years, according to the geological evidence.
• The larger picture in terms of plate tectonics. Which part of the Pacific Northwest is at a plate boundary, what kind of plate boundary is it, and what are its seismic hazards? Where do you live relative to that part of the state which is directly in the realm of this plate boundary?

Note that USGS and research consortium maps of faults active in the Quaternary period (the last 2 million years or so) may seem rather conservative and incomplete. These institutions hold high standards and require that definitive studies be published, demonstrating and detailing the existence of active faults, before they include them on their maps. Some faults, such as the unnamed fault near Entiat, are not on those official maps. In such cases, it may be that nobody has demonstrated just where those faults are on a geologic map, nor shown exactly which type of fault they are. Such unmapped faults, some of which are associated with microseismic activity that is being recorded on modern seismographs in the area, can still be considered as active faults or fault zones for the purpose of assessing seismic hazards in your area.

III. Virtual Field Site Questions

Tour the Emmons Glacier Virtual Field Site and answer the following questions.

8. Print the picture labeled Avalanche Deposit on Till. On it clearly circle and label the following: (1) avalanche deposit, and (2) till.
   
9. Print the picture labeled Lateral Moraine. Draw arrows pointing to and clearly labeling (1) lateral moraine, and (2) terminus (bottom end) of Emmons Glacier.
   
10. On the printout of the Lateral Moraine picture, draw a clearly visible line extending left from the lateral moraine showing about how high the top of the glacier was at maximum.
    
    Follow the instructions from your current course for submitting your lab diagrams.

Tour the Enumclaw Virtual Field Site and answer the following questions.

11. What was the Osceola Mudflow? Describe it and explain it.
12. When did the Osceola Mudflow occur, relative to the Vashon glaciation of the Puget Sound region?
    What evidence is there for this relative age relationship that is visible in a picture from the Enumclaw virtual field site?

Tour the Steamboat Rock Virtual Field Site and answer the following questions:

13. What type of unconformity is the contact between the granite and the basalt?
14. For the basalt lava to flow directly on top of the granite, what must have happened during the interval of geologic time after the granite formed and before the basalt erupted?
15. According to the theory of J Harlan Bretz, which has been proved to be essentially true, how did the Grand Coulee form?
16. What evidence is there of high-energy flow of liquid water in any of the pictures, not including the eroded coulees themselves?
17. Describe another possible way that the granite boulders might have come to rest on top of Steamboat Rock, instead of being deposited on till at the margin of a glacier. (Hint: How did pieces of Montana come to rest in the Willamette Valley of Oregon?)

Return to schedule