Laboratory Exercise 4 Volcanoes.docx

Laboratory Exercise 4: Volcanoes Volcanoes are one of Earth’s more spectacular geologic phenomena. Volcanoes can be awe-inspiring, terrifying and in many cases, dangerous. The discrepancy between the types of eruptions often dictates our perception of volcanoes. The economy of the Hawaiian Islands thrives on tourism directed to the spectacular beauty of the island chain and the relatively peaceful erupting lava fountains on the big island of Hawaii. Many of the more scenic mountains on Earth are of volcanic origin. Some of these mountains are still actively erupting volcanoes, whereas others are long dormant. In this laboratory exercise you will use Google Earth to visit volcanoes around the world. Some of these will be active volcanoes such as Mt. Etna, whereas others will be cinder cones or shield volcanoes. The shape of a volcano gives us evidence to interpret they type of magma that formed the volcano. By comparing the shape of the volcano with its location relative to plate boundaries, we are able to make inferences concerning the magma type and explosiveness of expected eruptions. When this information is integrated with the distribution of human population centers, we can begin to assess the risk posed by volcanoes to human property and lives. Learning Objectives After you have completed this laboratory exercise, you should be able to: 1. Identify the generalized types of volcanoes based on their shape 2. Make inferences concerning magma type and explosiveness 3. Explain the dangers associated with each eruptive style 4. Assess potential danger to human life and property for selected volcanoes Exercise A: Major Generalized Types of Volcanoes Shield Volcanoes Shield volcanoes are named for their gently sloping sides that result from the extrusion of low viscosity basaltic lava. The largest shield volcano on Earth is Mauna Loa that forms part of the Big Island of Hawaii. Mauna Loa extends some 30,085 feet from its base on the ocean floor to its summit. Only 13,677 feet of Mauna Loa is above sea level. Other important shield volcanoes include the Canary Islands, Iceland, Galapagos Islands, Easter Island, Sierra Grande, New Mexico, Mt. Wrangell, Alaska, Mt. Washington, Oregon, Payún Matrú, Argentina, and Olympus Mons on Mars. Olympus Mons, is some 80,000 feet tall and 300 miles wide at its base, a size that dwarfs shield volcanoes on Earth. Figure 1. Schematic profile of a Hawaiian shield volcano from Tarbuck et al., 15 th ed. 1

Figure 2. Lava fountain from Kilauea, Hawaiian Islands. This spectacular eruption ceased in the early 1980s. Figure 3. Diagram comparing scales of different volcanoes. A. Profile of Mauna Loa, Hawaii, the largest shield volcano and tallest mountain (above base) on Earth. B. Profile of Mt. Rainier, Washington. C. Profile of Sunset Crater, Arizona, a typical cinder cone. Notice how Mt. Rainier dwarfs Sunset Crater and how Mauna Loa is much taller and wider than Mt. Rainier. Figure 6.13 from Tarbuck et al., 15 th ed. 2

Figure 4. NASA image of Olympus Mons on Mars with the outline of Arizona superimposed. This huge shield volcano would stretch the distance between Stillwater, OK and Amarillo, TX. One reason Olympus Mons is much larger than shield volcanoes on Earth is that the surface of Mars does not have moving tectonic plates. If the Pacific Plate on Earth were stationary, all of the lava that formed the Hawaiian Islands and the seamounts to the north could have accumulated as one large volcano. Figure 5. Sierra Grande peak near Capulin, New Mexico is a classic shield volcano with gently sloping sides. 3

Composite Volcanoes Composite or stratovolcanoes are the tall steeply sloping cones that are commonly featured in images of the quintessential volcano. Many images in books or magazines articles concerning dinosaurs will feature a smoking composite volcano as background. Shield volcanoes owe their shape to alternating layers of lava and tephra (cinders and ash) produced by eruptions. Important and famous composite volcanoes include Fujiyama, Japan, Cameroon, Cameroon, Kilimanjaro, Tanzania, Citlaltépet, Mexico, Rainier, Hood, St. Helens and Adams, Washington, Mayon and Pinatubo, Philippines, Ararat, Turkey and Eyjafjallajökull, one of many unpronounceable volcanoes in Iceland. Famous historical composite volcanoes include Krakatoa and Tambora in Indonesia, Pele in Martinique, and Etna, Vesuvius and Stromboli in Italy. Figure 6. Schematic diagram of composite or stratovolcano with cone constructed of layers of pyroclastic material such as cinders, bombs and ash that alternate with lava flows. These volcanic cones are steep-sided and reach high elevations above the surrounding countryside. As a result, they are often snow-capped mountains. Figure is from Tarbuck et al., 15 th ed. 4

Figure 7. Mt. Rainier, a currently dormant composite volcano located some 33 miles southeast of Tacoma, Washington. Figure 8. Mt. Etna on the Italian island of Sicily providing another spectacular nighttime eruption. Etna has erupted for hundreds of thousands of years. Since man has sailed the Mediterranean Sea, Mt. Etna has served as a natural navigation beacon. 5

Figure 9. Mt. Fujiyama, the quintessential composite volcano with a snow-capped summit. City of Fuji in foreground. Cinder Cones Cinder cones are the most common type of volcanic eruption on Earth. These small cones (typically <1500 feet tall) are composed almost entirely of cinders and small bombs. Cinder cones often have accompanying basaltic lava flows that emanate from the base of the cone. Famous cinder cones include Sunset Crater, Arizona, Capulin in New Mexico, Parícutin in Mexico and Lava Butte in Oregon. Figure 10. Actual cinder cone and schematic. Cinder cones are small accumulations of mostly cinders (scoria) and typically have associated basaltic lava flows. Figure is from Tarbuck et al., 15 th ed. 6

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help