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Frank Press • Raymond Siever • John Grotzinger • Thomas H. Jordan

Understanding Fourth Edition

Chapter 6:

Lecture Slides prepared by Bill Dupré • Peter Copeland

Copyright © 2004 by W. H. Freeman & Company

4. …accumulating on the surface to form a Types of . • Basaltic lavas: low- lavas, 3. Lavas erupt from typically erupted at 1000o to 1200o C; cool to the chamber form . through central and side vents… • Rhyolitic lavas: high-viscosity lavas, typically erupted at 800o to 1200o C; cool to 2. …rises through the to form a form . • Andesitic lavas: intermediate in composition 1. Magma, which and viscosity between mafic and felsic originates in the ; cool to form . partially melted Fig. 6.1

Flood of the Columbia Types of Basalts • Flood Basalts: thick, widespread accumulations of basalt, typically fed by fissures • Pahoehoe: a very low viscosity basaltic characterized by a ropy texture • Aa: a relatively low viscosity basaltic lava characterized by a jagged, blocky texture • Pillow Basalts: a basaltic lava extruded beneath the , characterized by glassy pillows filled with crystalline basalt Fig. 6.2 Vesicular Basalt: trapped gases form bubbles (vesicles)

Fig. 6.3 Fig. 6.4

Pyroclastic Volcanic Bomb Material:

Fragmentary volcanic rocks ejected into the air

Fig. 6.5 Fig. 6.6

Volcanic Features Formed by Pyroclastic Flows: Central Eruptions

A flow consisting • Shield Volcanoes of a hot (up to 800o C), • Volcanic domes poisonous mixture of gas and pyroclastic material • -cones Volcanoes moving downslope at • Composite Volcanoes speed in excess of 200 • Craters km/hr! •

Fig. 6.8 Eruptive Styles and

Volcanic Dome

Mauna Loa Volcano

Composite Volcano

Crater Fig. 6.9 Fig.6.9.a

Shield Volcano

Lava Dome

Fig. 6.9b

Fig.6.9.a Lyn Topinka/USGS

Volcanic Dome Cinder Cone, near Managua, in 1968

Fig. 6.9b Mark Hurd Aerial Surveys Fig. 6.9c Cinder Cone Mt Fujiyama, Japan

Fig. 6.9c Raga/The Stock Market Fig. 5.15

Caldera

Stages in the Development of Crater

Fig. 6.10

Shiprock, Formation of a Diatreme

Fig. 6.12 Fig. 6.12 Fissure Eruptions Volcanoes along the Fissure A volcanic eruption originating () formed in 1783, resulting along an elongate fissure rather in the largest lava than a central vent. flow in recorded history

Fig. 6.13

Mt. St. Helens: Before Mt. St. Helens: During

Hydrothermal Activity: • The circulation of water through hot -encrusted volcanic rocks and magma •Forms – volcanic vents emitting gases, some charged with dissolved •Forms – heated hydrothermal under pressure, that intermittently erupts at the surface • Provides the source for Geothermal . Fig. 6.16 Volcanism Associated with Plate

Fig. 6.19 Fig. 6.20