GLY July Ms. Nelda Breedt. Plates move slowly and eventually.

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1 GLY 162 Tectonic Processes: Volcanism Ms. Nelda Breedt GLY 162 Environmental Geology Plate Tectonics Plates move slowly and eventually. 2 Spread apart (divergent plates) Dive beneath one another (converging plates) Crumple together (converging plates) Leads to volcanism and earthquakes. 1

2 GLY 162 Primary Hazards 3 Seismic Magmatic 4 Volcanism Vulcan - Roman god of fire Places where molten rock and gases exit Earth s (or another planet s) surface are called volcanoes. 2

3 GLY Volcanism 800 active volcanoes on Earth Mainly around Pacific Ocean & volcanic islands Specific localities: Mid Ocean Ridges Large fracture zones on continents Land side of subduction zones Hot spots (plumes) Volcanism 6 3

4 GLY Explosive / Non-explosive Controlled by magma type and dissolved gas content. 8 Explosive / Non-explosive 4

5 GLY Volcanic Material Viscosity depends on Composition (esp. Si) Gas content (H 2 O, CO 2, SO 2,...) Temperature (eruption temperatures: ºC) Si-rich (rhyolitic / felsic) High viscosity (SiO 4 -polymerisation) Si-poor (basaltic / mafic) Low viscosity Same lava, different temperature 10 Viscous aa flow (1989) Less viscous pahoehoe flow (1959) 5

6 Viscosity units GLY Lava Viscosity % SiO 2 (by weight) 12 Volcanic Material Magma becomes lava when reaching the Earth s surface Composition (% of volcanoes worldwide): Basaltic (80%) Andesitic (10%) Rhyolitic (10%) 6

7 GLY Volcanic Material 14 Remember: Rhyolitic volcanoes primarily on continents Andesitic volcanoes on continents and in oceans Basaltic magma also erupt on continents and in oceans Melting of continental crust rhyolitic magma Mantle source of andesitic & basaltic magmas 7

8 GLY 162 Volcanic Material Hazards Primary Effects Lava flow Move slowly (few km/h with ºC) Predictable flow path: valleys, low lying areas 1999 John Wiley and sons 8

9 GLY Hazards Primary Effects Pyroclastic activity High Si-magmas & explosive volcanism Ash to larger particles (bombs) Atmospheric pollution - low visibility Cover large areas Destroy vegetation, blocks rivers Contaminate surface water Block animal digestive systems Suffocation 18 Hazards Primary Effects 1999 John Wiley and sons 9

10 GLY Hazards Primary Effects Pyroclastic flows Hot gases and fine ash particles (600 >1 000ºC) Flow down mountain side at high speeds (> 100km/h) If mixed with water: Lahar (volcanic mudflow) 20 Lake Nyos, Cameroon, 1986 Poisonous gases Devastation downwind of volcano H 2 S, CO 2, SO 2, CO Death valleys 1999 John Wiley and sons 10

11 GLY Hazards Primary Effects Magma-water interaction/ phreatomagmatic eruptions Volcanic islands, watermagma contact Krakatoa, Indonesia (1883) 100 million t dynamite Tsunamis killed people Santorini, Greece 1400 BC Minoan civilization 22 Hazards Secondary Effects Fires Tsunamis Floods Mass movements (mudflow lahar) Down slope movement of saturated pyroclastic material Earthquakes Climate and Atmospheric Chemistry 1999 John Wiley and sons 11

12 GLY 162 Hazards Secondary Effects 23 Tracking the path of sulphuric acid mist from Mt Pinatubo SO 2 aggravates ozone depletion! 1999 John Wiley and sons 24 Other Effects Alter chemistry of atmosphere Block Sun s radiation (global cooling) Periods of darkness Blockage of river channels Acidic precipitation (aerosols) Highly fertile soils Addition of land Spectacular sunsets Magnificent scenery 12

13 GLY Prediction Classification: Active: Erupted in recent history Dormant: inactive, but potential to become active Extinct: No recent eruption, eroded Identify past eruptive style! Warning signs: Seismic activity (earthquakes) Bulging / tilt / uplift Water temperature Gases Magnetic anomalies 26 Land-use Planning Around active volcanoes: Evacuation plan Danger / hazard zones Protection structures (retaining walls, etc.) Land-use regulations Prediction 13

14 GLY Land-use Planning 1999 John Wiley and sons 28 Volcanism as a Resource Initial origin and evolution of our atmosphere 14

15 GLY 162 Volcanism as a Resource Fertile soils Volcanism as a Resource Forms mineral deposits 15

16 GLY 162 Volcanism as a Resource Geothermal energy Volcanism as a Resource Creates new land 16