SolidEarth2

SolidEarth2 - Crustal cycling creates plate boundaries...

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1 “Solid” Earth: Global Tectonics (2) Jeff Dozier & Tom Dunne Fall 2007 Crustal cycling creates plate boundaries From: This Dynamic Planet, US Geological Survey: www.usgs.gov Types of Plate-tectonic Environments Influence Landscape Characteristics and Functioning (2) Ocean-ocean Island arcs Plate environment Landscape type Convergent margins Ocean-continent Continental-margin mt. rges. Continent-continent Collisional mountain ranges Transform margins Low mountain ranges Ocean-ocean plate convergence with subduction constructing island arcs Two oceanic lithospheric plates meet One has traveled further from its spreading center Is older, colder, denser Sinks and melts Magma (molten rock) rises to surface in a line of volcanoes, which eventually break the ocean surface http://pubs.usgs.gov/publications/text/understanding.html#anchor5798673 Ocean-ocean convergence constructing island arcs Zandt, Nature , v 416, 2002 Ocean-continent subduction can also construct island arcs
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2 Ocean-ocean and ocean- continent island arcs: trenches and island arcs f the western Pacific of the western Pacific Formation of land in island arcs Sakurajima Volcano, near Kagoshima, Japan Melting of subducted ocean crust plus overlying sea-floor sediments Æ explosive volcanism, producing fragmental, weak rocks that rode rapidly in wet climates erode rapidly in wet climates. Island arcs have little low- gradient land, except that which has been built by catastrophic sedimentation from landsliding and volcanism. Note limited space for settlements Flood and sedimentation hazard around Mt Usu, Japan after 1983 eruption Flood and sedimentation hazard around Mt Usu, Japan after 1983 eruption Mt. Pinatubo (Philippines) caldera after eruption of 1983 Debris flow and flood deposits after Mt. Pinatubo eruption, viewed from rim of caldera
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3 Urban areas inundated by debris flow deposits after eruption of Mt. Pinatubo Landscape Functioning: Island arcs Young and even older volcanic rocks in dormant volcanic mountain ranges (e.g. Japanese Alps) Mechanically weak, fractured and fragmental rocks on steep slopes collapse as landslides during typhoons High sediment supply to rivers Rivers carry high flood discharges and sediment loads downstream to lowlands High population densities confined to narrow lowlands around edges of active and dormant volcanic ranges Natural hazards a dominant concern in environmental management Ocean-continental plate convergence http://pubs.usgs.gov/publications/text/understanding.html#anchor5798673 Ocean-continent Convergent Plate Boundaries Subduction movie courtesy of Prof. Tanya Atwater, Dept. of Earth Science, UCSB Subduction – Oceanic lithosphere is denser than continental lithosphere.
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SolidEarth2 - Crustal cycling creates plate boundaries...

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