Volcanic Activity. 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,
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.
(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.
GasCarbon (monoxide/dioxide); hydrogen; sulphur dioxide- propel magma to the surface.
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.
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
Very large layer (20km) ….. batholith… magma forced to crust & melts rock. Result is area sinks… large dip….eg. Leinster batholith.
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.
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
Geysir, bubbling mudpools attract tourists
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.