Answer the following Questions for Review
(Chapter 6, page 146)
What can happen to heat, pressure, and water content to melt rock and create magma? (1) Add heat, decrease pressure, or add water to cause melting.
What factors control the violence or style of an eruption? (2) The amount of water, viscosity of the magma, or composition and amount of magma. What properties of basalt magma control its eruptive behavior? (3) Low water content and low viscosity.
What properties of rhyolite magma control its eruptive behavior? (4) High water content and high viscosity. What drives an explosive eruption? (5) The steam. How does pahoehoe lava differ from aa lava? (6) Pahoehoe is ropy-looking and lava is clinkery. On a huge shield volcano, such as Mauna Loa, what is the main type of eruptive site? Where on the volcano is (or are) such a site (or sites)? (7) Eruptions produce basalt lava flows that build the main visible mass of the volcano. Yellowstone National Park has two huge calderas, each more than 20 km across. How do such calderas form? (8) Ejection of a large volume of magma often causes collapse into the magma chamber. Why do shield volcanoes have such a different shape than stratovolcanoes? (10) Shield volcanoes are basalt eruptions of very fluid basalt lava within a small area that will eventually build a gently sloped pile
of thin flows. The thin flows are caused by their low viscosity, low volatile content, broad and gentle sloping sides, and large volumes. The stratovolcanoes are moderate size and volume, moderate viscosity
and slope, and moderate to large volatile content. The lava is not exactly fluid. Flowing on only steep slopes before cooling and solidifying. On what type of plate boundaries are volcanoes typically found? Explain how each of these tectonic environments give rise to volcanoes. (14) Volcanoes are typically found on spreading zones, subduction zones, or hot spots. Typically these areas are known to have major changes in temperature, pressure, or water content, which allows rocks to melt and the volcanoes to form.
