Chapter 9 Volcanic Processes PRELAB STUDY SESSION In preparation to this exercise, briefly answer the following questions. Refer to your textbook for the information you need. In addition to these questions, your lab instructor might give you more questions to answer. A. List and sketch the various type of volcanoes. Sketch them to scale with respect to each other. B. What materials can a volcano erupt? It is not just lava. List volcanic products by composition and by type (tephra, size, volcanic gases, etc.). C. Name some possible volcanic hazards. D. The differences in volcanic behavior are due to the combination of many elements such as magma chemistry, volatiles in the magma, type of volcanic structure, and tectonic settings. How can we study what volcanoes are doing? How can we deduce out what a volcano will do? Prior to the 1980 eruption, MSH had a conical, well-defined shape. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 × 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Go to the Cascade Volcano Observatory website to see images of MSH before and after the eruption: http://volcanoes.usgs.gov/volcanoes/st_helens/st_helens_multimedia_gallery.html Table 9.2 summarizes the eruptive history of MSH starting from the eruptions that crop out at the base of the “recent” MSH. The eruptive episodes are grouped by duration and eruptive characteristics. The table is based on data compiled by the Global Volcanism Program of the Smithsonian Institution from published scientific literature on MSH. Starting dates of eruptions were calculated by dating techniques such as radiocarbon, tephrochronology, and dendrochronology. Historical records are available only for the most recent eruptive episodes. When possible the VEI was calculated. 2. Using the data available in Table 9.2 to answer the following questions: a. What are the common traits of MSH eruptions with respect to the VEI, type of eruptions, site of eruption, volcanic materials erupted, and mode of emplacement (e.g., type of flows)? Which ones are most common? Summarize your observations. b. Does MSH eruptive history suggest that the 1980 eruption was to be expected? What other visual and geophysical monitoring helped forecast the eruption? Read the paragraph “precursory activity” at: http://volcanoes.usgs.gov/volcanoes/st_helens/st_helens_geo_hist_99.html What were the most compelling evidence that the eruption was imminent? c. Which one was the largest eruption on record? Volcanic Processes 9-5 3. The eruption of May 18, 1980 produced dramatic changes in the shape and volume of MSH using the preeruption topographic maps (Figure 9.1) build a North-South topographic profile that cuts across the summit (9677 ft). Use only the index contour lines (CI 400 ft). Construct a second topographic profile along the same line using the posteruption map (Figure 9.2). Note that this map has index contour at 200 CI. You can build the profiles on the same graph so they will overlap. A map with both before and after eruptions contour lines can be found at https://pubs.usgs.gov/imap/1411/plate-1.pdf Be mindful of the scale and index contour when building the topographic profile. a. Compare the two profiles describe what changes have occurred along the profile 4. MSH before the eruption had a regular cone shape, with a base-diameter of about 6 km and an elevation of about 3 km from the surrounding area. The preeruption volume of the volcano can be approximated to that of a cone: V = 1/3 q R2h (where R is the radius and h is the height). a. Using the formula for the volume of the cone, calculate the volume of pre-1980 MSH in cubic kilometers. Show your calculations. b. The 1980 eruption removed about 6.5 km3 of the volcanic edifice, what percentage of the volcano does was then removed by the eruption? Show your calculations. 9-8 Chapter 9 Student Name Lab section Date c. Convert the total volume of lava + tephra erupted in 1980 in cubic kilometers (see Table 9.2). What is the total volume of material produced by the eruption (Note: This is juvenile material, freshly produced by the volcano.) d. How does the 1980 eruption of juvenile material compare to the other eruptions of MSH (see Table 9.2)? 9-11 Student Name Lab section Date 5. Like any other active volcano, MSH needs to be closely monitored in order to assess the level of activity and the likelihood of an eruption. To see what physical parameters are been monitored at MSH go to: http://volcanoes.usgs.gov/volcanoes/st_helens/st_helens_monitoring_16.html a. List the physical parameters that are monitored by Cascade Volcanological Observatory. Which ones need sensors on the ground, which ones are detected by remote sensing? b. What was the depth of the earthquakes in 1980? When were earthquakes at that depth observed again? c. What is the other typical depth of earthquakes at MSH observed during the 1980–2012 interval and what does it indicate? d. Return to the main monitoring page for MSH. Scroll below the instrument map to see the depth of the earthquakes recorded this week. What is the number of earthquakes observed, what is their depth? e. What deformation of the ground characterized the 2004–2008 eruptive episode of MSH and what did it indicate about the internal processes of the volcano? f. What does the volcanic gas SO2 indicate about the movement of magma? g. What trends in SO2 emission have been observed at MSH? Student Name Lab section Date VOLCANIC HAZARDS Volcano Alert Level Land Based Volcanic activity may hinder or compromise human life or interest, so volcanic activity is often recognized as a geologic hazard. The United States Geological Survey (USGS) runs the volcanological observatories of the United States and it is part of the World Organization of Volcanological Observatories. The international community recognizes found levels of alert that are meant to inform people on the ground about volcanic activity. The alert levels are issued in conjunction with the aviation alert code because aircraft is especially vulnerable when flying into dispersed volcanic ash, virtually invisible to the radar onboard. Alert codes are summarized in the table below: Aviation Color Codes Normal Advisory Watch Volcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to non-eruptive background state. Volcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase. Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway but poses limited hazards. Warning Hazardous eruption is imminent, underway, or suspected. If possible Specify Plume height Green Yellow Orange Red 6. Visit the USGS Volcano Hazard page at: http://volcanoes.usgs.gov/. Answer the following questions: a. How many volcanoes are reported on Red alert? ____ on Orange? _____ How many on Yellow?_______ b. Where are these volcanoes located? Use the mute map of the World to mark the position of the volcanoes currently on high level of alert. Student Name Lab section Date VOLCANOES OF THE WORLD The Global Volcanism Program of the Smithsonian Institution in collaboration with the USGS publishes a weekly bulletin of ongoing volcanic activity. Visit the page: http://volcano.si.edu/reports_weekly.cfm 7. Choose a volcano from those actively erupting this week. Make sure it is a volcano you never heard about before (learn something new!) and it was not mentioned previously in this exercise. Click on the symbol to access the volcano info page and answer the following questions. a. What is “your” volcano name? b. Where is it located? (region and Nation in the World). Plot the position of your volcano on the map at the end of the chapter. c. What type of volcano is this? (summarize the description) d. What type of eruptions are typical of your volcano? e. What is its highest VEI on record? f. When did it erupt last time? Student Name Lab section Date g. Are other volcanoes found in the same region? Why is this volcano there? (a plate boundary, a hot spot? etc.) Student Name Lab section Date 9-19 Hesitant, concept is unclear, would not know how to use/apply I have a general idea of what this is about and with guidance I could apply what I learned to problem solving Level of Confidence I am confident I understand this topic and I can apply it to solving a problem Lab section What challenged/interested you the most about this activity? Why? How challenging did you find this exercise? Appreciate the significance and supporting evidence related to assessment of natural hazards From field measurements estimate quantitatively the changes in the landscape (topographic profiles before and after eruption, and calculation of volume) Evaluate data collected from diverse sources (historical, field evidence, diverse dating techniques, V.E.I.) in describing eruption history of Mount St. Helens (or any other volcano) Learning Objective Laboratory Experience Assessment: Volcanic Processes—The Mt. St. Helens Case Study Student Name Date

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