Lecture Outlines Physical Geology, 14/e Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Plummer, Carlson & Hammersley

Volcanism and Extrusive Rocks Physical Geology 14/e, Chapter 4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Atmosphere – originally created from gases released from volcanic eruption Hydrosphere – produced by condensation of volcanic water vapor Biosphere both positively and negatively influenced by volcanism lava flows and ash weather to produce fertile soils violent eruptions can destroy nearly all life in their paths large amounts of ash and volcanic gases in atmosphere can trigger rapid climate changes and contribute to mass extinctions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Volcanism & earth’s systems

Lava – produced when magma reaches Earth’s surface explosive eruptions can produce rapidly cooled rock fragments called pyroclasts, size ranges from dust (ash) to boulders (blocks and volcanic bombs) calm oozing of magma out of the ground produces lava flows pyroclastics and lava flows form extrusive igneous rocks lava flows and pyroclasts pile up to form volcanoes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Volcanic eruptions

Mythology, religion and volcanoes Hawaii – Pele, Iceland – Loki Growth of volcanic islands (Hawaii) Geothermal energy natural steam harnessed as clean energy resource Climatic effects very large eruptions can result in measurable global cooling resulting crop failures and famines Volcanic catastrophes Mt. St. Helens, Pompeii, Krakatoa, Tambora, Crater Lake Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Living with volcanoes

Violence of eruptions controlled by: dissolved gases in the magma ease/difficulty of gases escaping to atmosphere Viscosity - a fluid’s resistance to flow higher silica contents produce higher viscosities cooler lavas have higher viscosities amount of dissolved gases, the more dissolved gases, the more fluid the lava Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Eruptive violence & physical characteristics of lava

Scientific Investigation of Volcanism rocks, gases and events from observed eruptions compared to similar lavas elsewhere to infer the nature of past activity Rock Composition lightrhyolite - high silica; light color darkbasalt - low silica; dark color andesite - intermediate silica and color Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Extrusive rocks and gases

Vent - opening through which lava erupts Crater - basin-like depression over the vent at the summit of the volcano Caldera - volcanic depression much larger than the original crater, having a diameter of at least 1 km Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Volcanic landforms

Shield volcanoes broad gently sloping composed of solidified lava flows flows often contain lava tubes Cinder cones small steeply sloping composed of a pile of loose cinders Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Types of volcanoes

Composite volcanoes aka stratovolcanoes moderately to steeply sloping constructed of alternating layers of pyroclastic debris and solidified lava flows composed primarily of intermediate composition volcanic rocks (i.e., andesite) most common type of volcano at convergent plate boundaries Volcanic domes extremely high viscosity, degassed, felsic lavas (often glassy, e.g., obsidian) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Types of volcanoes

Flood eruptions very fluid (basalts) extremely large in volume create extensive lava plateaus eruption times correspond with largest mass extinction events Submarine eruptions nearly always basaltic mid-ocean ridge eruptions pillow basalts Columbia river flood basalts Pillow basalts Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Other eruption types

Shield volcanoes Venus, Mars, Io Lava domes Venus, Moon Flood eruptions very fluid (basalts) extremely large in volume extensive flat lava plains (Moon, Mars, Venus, Mercury?) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Volcanism on other planets

End of Chapter 4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.