文档介绍：Chapter 5: Magma And Volcanoes
Introduction: Earth’s Internal-- Thermal Engine
Magma is molten rock beneath Earth’s surface.
Because liquid magma is less dense than surrounding solid rock, and obviously more mobile, magma, once formed, rises toward the surface.
Magma that reaches the surface does so by erupting through vents we call volcanoes.
Volcanoes
The term es from the name of the Roman god of fire, Vulcan.
There are different types of volcanoes.
Eruption vary from gentle flows (Hawaii and Iceland) to catastrophic explosions (Mount St. Helens, Mt. Pinatubo, Soufriere Hills).
The majority of eruption never make the news because they occur beneath the ocean, unobserved.
Magma
Magma has a wide range positions, but silica (SiO2) always dominates the mix.
Magma has high temperatures.
Magma is fluid—it has the ability to flow.
Most magma actually is a mixture of liquid (often referred to as melt) and solid mineral grains.
Composition of Magmas and Lavas
position of magmas and lavas is controlled by the most abundant elements in the Earth—Si, Al, Fe, Ca, Mg, Na, K, H, and O.
Three distinct types of magma are mon than others:
Basaltic, containing about 50 percent SiO2.
Andesitic, about 60 percent SiO2.
Rhyolitic, about 70 percent SiO2.
The three main Magmas
Basaltic Magmas
Basaltic magmas are erupted by approximately 80 percent of volcanoes worldwide (the seafloor worldwide is mostly basalt).
Magma from Hawaiian volcanoes such as Kilauea and Mauna Loa is basaltic.
The entire island of Iceland is basaltic.
Andesitic and Rhyolitic Magmas
Andesitic magmas are about 10 percent of the total magma.
Magma from Mount St. Helens in Washington State and Krakatau in Indonesia is usually andesitic.
Rhyolitic magmas are about 10 percent of the total magma.
Magmas erupted from volcanoes that once were active at Yellowstone Park are mostly rhyolitic.
Very viscous magma slow moving, from Kilauea Volcano in Hawaii in 1989
Fast flowing lava, low viscosity basalti