Transcript Slide 1
Volcanic eruption- solid, liquid or gas forced to earths surface. Concentration of volcanic activity at plate boundaries - Pacific Ring of Fire Magma rises through mantle, pressure reduces so gases exapnds forcing magma upwards, forms in magma chamber-temp 1200°C, pressure becomes too much and eruption occurs Major volcanoes occur where plates (i) converge (ii) diverge (iii) hotspots. Lava (i) Pahoehoe lava (Basic) Slow moving, hot (1000˚C), runny, low in silica so gas can escape easily .... Cools slowly - flows over long distance & creates sloping landforms. (ii) Viscous Lava (Acid) Pasty, high silica content, gas cannot escape, gives violent eruptions. Cools quickly & travels shorter distances - steep landforms. Gas Carbon (monoxide/dioxide); hydrogen; sulphur dioxide- Rock: Pyroclastic material…. Ash, cynders, & large particles. Nuee Ardente…. Flows of gas, steam, dust & fine particles…. Speed of 500kmph & up to 1000kmph at source. Dust blocks sunlight causing temp. change. Volcanoes at divergent margins: Flows freely through Fissure e.g. Surtsey, Kilimanjaro 1. Mid Ocean Ridges 2. Fissure eruptions … large volumes of lava gently flows to surface from a crack. - plateaux. Eg. Antrim Plateaux & Columbia Plateaux (usa) Volcanoes at Convergent Margins 1. Central vent - Lava from central vent creates cone shaped mt. (crater) Caldera… top blown off then sealed. New cone dev. parasitic cone - Secondary vent emits gas & steam- fumeroles eg. Japan 2. Cinder cone - lava bursts into air & falls back around cone… steep sided with gentle base e.g. Parcutin, Mexico. 3. Composite volc. - layers of lava & pyroclastic material … steep slope.. Several vents - violent eruptions eg. Etna & Vesuvius. 4. Dome cone.. Thick lava, bulbous shape… blocks vents & traps gas… erupts destroying itself eg. St Helens USA. 5. Shield… build up of successive slow lava flows … broad base & gentle slope… gentle eruptions flow down the side of volc. Eg. Mauna Lao, Hawaii Hot springs & Geysers…(i) water & material mix creating a spring eg. Blue Lagoon , Iceland. (ii) eject with force - geyser (steam & water) eg. Lanzorote. Hotspots…thermal plume forces its way through fault in crust, magma erupts onto the surface, creates volc…. Plates move and creates new volc. = islands. Eg. Hawaii, (Mauna Loa still active) Caldera…large crater, violent eruption may remove summit of volcaone causing it to collapse- often filled with a lake e.g. All above are Extrusive Feature i.e. on the surface Intrusive: Magma forced into crust by pressure- Plutons Dyke .. Vertical… magma into fractures Sill.. Horizontal.. btw. Layers of sedimentary rock… near surface. Layer arched up…...laccolith down… lopolith… Very large layer (20km) ….. batholith… magma forced to crust & melts rock. Result is area sinks… large dip….eg. Leinster batholith. 1. Active…currently erupts… Mt Etna, Sicily 2. Dormant.. Not presently erupting but may in future… St Helens, USA 3. Dead… has erupted but not likely to erupt again. Eg. Slemish Predicting vol: (i) Seisomoter- records tiny earthquakes as magma rises (ii) Lasers-- detect swelling of area (iii) chemical sensors-- detect sulphur dioxide. Negative Effects 1883 Krakatoa (Indonesia)- explosive volc…. Destroyed island & caused tsunami killing 36,000 & leaving dust cloud for 12 months. Caused a temp. drop of 2˚C 79AD… Vesuvius.. killed 2000 & buried Pompeii 1984- Columbia. Mud flow killed 21,000. Positive effects • Forms metals & gems- gold, copper, silver, mercury Eg. Kimberley, South Africa - volc revealed richest conc. of diamonds in the world. extreme heat (temperatures of 2200 degrees Fahrenheit) and extreme pressure cause carbon atoms to crystallize forming diamonds ninety miles under the earth's surface. Diamonds reach the surface of the earth via volcanic pipes, or channels or via placer, alluvial deposits. The diamond is the hardest of all known bodies •Tourist attraction…Yellowstone National Park, Wyoming, Montana and Idaho, employs 800, 2.8 million visitors, 287 campsites, 8900km squared. •Fertile soils… minerals give nutrients & dust, ash & cinders act as fertilizer. -- agric. dev. Eg. Java (India).. tea; Brazilian plateau—coffee •Thermal energy- harnessed for heat & electricity eg. Iceland Geothermal energy (hot water) Iceland. Iceland on Mid. Atlantic Ridge… water is superheated by magma.. Over 100˚C…> stays as liquid due to rock pressure. Used as energy source & reduces fuel imports. Hengill Volcano 26% of Icelands power generated by geothermal energy 89% of Icelands home heating is geothermal in origin Nesjaviller Power Plant – most powerful geothermal plant in the world First opened in 1965 – deepest hole is 1.4 miles 200˚C… cold water pumped in steam - electricity. Steam piped & heats a lake. Lake water 80˚C used as domestic heating in Reykjavik. Source of clean water, less pollution. Water then piped to greenhouses - allows year round veg. & flowers. Also hot spas as tourist attraction eg. Blue Lagoon near Reykjavik Ireland & volc. activity Antrim Derry Plateau 4,000km² 65 to 15 m yrs ago American & Eurasian plates moved apart. Lava flowed gently to form basalt. Tectonic uplift formed plateau eg. Giants causeway. Basalt hexagonal columns formed as magma cooled slowly. Slemish Co Antrim - volc. plug, denuded by weathering. Carrrickarede - volc. rock rises vertically through chalk (proof of volc. site) Mourne Mts: magma rose but remained beneath surface , now weathered Leinster Batholith Largest in Ireland & Br. 120kms Dub to Kilkenny. Including Dub/Wicklow & Blackstairs mts. Granite domes formed during caledonian folds. Magma occupied the arched folds… since weathered to give dome shaped mts.