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Vulkaniska and Tektoniska Landformer Kap 14 och Berg&Jord Geomorfologi • Geomorfologi – Den vetenskapliga studien av processer som skapar landskapsformer • Landformer – Den ytliga fenomen av jorden – Endogena (eng. initial) och exogena (eng: sequential) processer/landformer Endogena och exogena landformer En sprickdal/gravsänka (rift valley) I närheten av Quilotoa, Ecuador Vulkanisk Aktivitet • Vulkaner – Endogen landform – Stratovolcanoes are cone shaped – Shield Volcanoes are dome-shape. Stratovulkaner • Formed of layers of felsic magma and tephra • Occur along subduction plate boundaries • Magma is generally very viscous and gassy. • Violent explosions where huge quantities of tephra are ejected along with white-hot gasses. • Steep-sided volcanic cone due to the gummy nature of the magma. • • • • Calderas Våldsamt vulkanisk eruption Centrala delen av vulkanen blir förstort Kollapse resulteras i en centralt depression: caldera Stora mängder av gas och damm I atmosfären Caldera av en stratovulkan i Alaska Satellite image of Santorini's caldera, formed around 1600 BC. Mt St. Helens, innan och efter 18 maj 1980 Var finns stratovulkaner? Stratovolcanoes are produced by the subduction of tectonic plates. Skjöld Vulkaner • Formed over a hot plume of mantle magma. • Composed of mafic magma which is thin and runny and flows easily. • Characterized by gentle slopes and broadly rounded domes. Platt rörelse över en Hot Spot Life Cycle of a Hotspot Volcano Basaltiska Landformer • Flood Basalts – Huge plains covered with basalts – Occur where a mantle plume lies beneath the continental lithosphere. Basaltiska Landformer • Cinder cones – Frothy basaltic magma is ejected under high pressure from a narrow vent, producing tephra. – Forms a small, circular hill with a central crater. Marion Island, skjöldvulkan över en Hot Spot i södra havet, här med cinder kon Global Volcanic Activity Volcanic Eruptions: A Natural Hazard • Release huge amounts of poisonous, incandescent gases that will kill living beings. • Ash, cinders and ejecta (tephra) bury objects in the area. • Hot lava destroys almost anything in their path. • Earthquakes • Tsunamis - Seismic sea waves • Lahars – • mudflows associated with volcanic activity, melting ice and snow Landformer av tektonisk aktivitet Two forms of tectonic activity: 1. Compression takes place when tectonic plates collide. 2. Extensional plate motion occurs along rifting plates. Fold Belts 4 typer av förkastning Normal förkastning • Result from extensional crustal movements. • Vertical movement of the two blocks exposes a fault scarp. • Multiple normal faults create horst and graben. Fault Block Mountains Transcurrent Faults • Also known as strike-slip faults. • Horizontal movement with little or no scarp produced. • Usually occur along the boundary of two tectonic plates. • The San Andreas Fault is the most famous. Öst-afrikas ”rift valley”: början av kontinentalt spridning Jordbävningar • A motion of the ground surface, ranging from a faint tremor to a wild motion capable of shaking buildings apart. • The center of an earthquake is the focus. • The motion is caused by slippage of large blocks of crust under extreme strain. • Volcanic events may also cause earthquakes. Richter Scale • Earthquakes are measured by the Richter Scale. • Each whole number increase is an energy release some 32 times greater. • The largest earthquake observed had a magnitude of 9.5 – Chile, 1960 Moment Scale Global Earthquake Activity • Red dots show earthquake centres originating between 0 and 100 km depths. • Black dots show earthquakes of magnitude 8.0 or greater during the past 80 years. Seismic Sea Waves • Tsunami are produced by a sudden movement of the sea floor near the earthquake centre. • Waves travel over the ocean with no discernible height. • Once the wave energy reaches the more shallow water of the coastline, a large, destructive wave, as high as 10 m is produced. • Flooding from these waves has killed tens of thousands of people. • Japan, 1703 - 100,000 people died.