Physical Geology, 15/e

Transcription

1 Lecture Outlines Physical Geology, 15/e Plummer, Carlson & Hammersley Copyright McGraw-Hill Education, Inc. Permission required for reproduction or display.

2 Volcanism and Extrusive Rocks Physical Geology 15/e, Chapter 4

3 Volcanism & Earth s systems 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

4 What are Volcanoes and Why Should We Study Them Volcanism occurs when magma makes its way to the Earth s surface Volcanoes landforms formed by the extrusion of lava. Lava produced when magma reaches Earth s surface Explosive eruptions produces rapidly cooled rock fragments called pyroclasts, size ranges from dust (ash) to boulders (blocks and volcanic bombs) Effusive eruptions - calm oozing of magma out of the ground produces lava flows

5 What are Volcanoes and Why Should We Study Them Creation of New Land Lava flows build up volcanic islands like Hawaii Geothermal Energy Underground heat generated by igneous activity Effect on Climate Very large eruptions can result in measurable global cooling resulting in crop failures and famines

6 Eruptive Violence and Physical Characteristics of Lava 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

7 The Eruptive Products of Volcanoes Effusive Eruptions Mafic Lava Flows low viscosity and flows easily Pahoehoe, A a, Lava Tube Flood Basalts very low viscosity and flows very easily from erupting fissures A a Pahoehoe

8 The Eruptive Products of Volcanoes Effusive Eruptions cont. Columnar Jointing parallel mostly six-sided vertical columns Submarine Lava Flows pillow structure formed as lava flows into water. Intermediate and Felsic Lava Flows thicker viscous lavas that flow short distances

9 The Eruptive Products of Volcanoes Explosive Eruptions Pyroclastic Materials Dust, ash, cinders, lapilli, blocks and bombs Pyroclastic Flows mixture of gas and pyroclastic debris that flows rapidly down slope.

10 Types of Volcanoes 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

11 Types of Volcanoes Composite Volcanoes 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 Distribution of Composite Volcanoes Circum-Pacific belt Mediterranean belt

12 Types of Volcanoes Lava Domes extremely high viscosity, degassed, felsic lavas (often glassy, e.g., obsidian) Calderas volcanic depression at least 1 km in diameter Result from very violent eruptions Crater Lake in Oregon is an example

13 Living with Volcanoes Volcanic Hazards Pyroclastic flows account for the largest number of deadly events - Pompeii Volcanic gases carbon dioxide, Nyos Cameroon Volcanic mudflows (Lahars), Armero Colombia Indirect hazards such as famine and lightning Eruption times correspond with largest mass extinction events Pompeii and Mt. Vesuvius

14 Living with Volcanoes Monitoring Volcanoes Volcano status Approximately 1500 potentially active volcanoes worldwide Active if currently or recently eruptive (Approximately 500 in the world today) Dormant if it hasn t erupted in many thousands of years but is expected to erupt in the future Extinct haven t erupted in many years and show no signs of any future eruptions. Hawaiian Volcano Observatory Cascade Volcano Observatory Hazard mapping

15 Extraterrestrial Volcanic Activity Shield Volcanoes Venus, Mars, Io Mons Olympus Lava domes Venus, Moon Flood eruptions very fluid (basalts) extremely large in volume extensive flat lava plains (Moon, Mars, Venus, Mercury?)

16 Plate Tectonics and Volcanism Volcanic Activity at Divergent Boundaries Decompression Melting Effusive eruptions of basaltic magmas and pillow lavas Formation of most of the sea floor Mid-oceanic ridges, Iceland Volcanic Activity at Convergent Boundaries Most large well-known volcanoes Explosive composite volcanoes Viscous andesitic lavas Within-Plate Volcanic Activity Mantle Plumes (Hot Spots) Hawaii, Yellowstone Basaltic magma/lava

17 End of Chapter 4