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Physical Geography: Volcanoes - Coggle Diagram
Physical Geography: Volcanoes
Formation of a volcano
Magma chamber from which molten magma moves
Vent
Crater
Volcanic cone
Pyroclastic material
Location of volcanoes
Pacific Ring of Fire
Divergent plate boundaries: fissures
Convergent plate boundaries: subduction zones
Hotspots: weakness in the centre of a plate over a plume of superheated magma
Life cycle of a volcano
Active, e.g. Mount Etna
Dormant, e.g. Mount St Helens
Extinct, e.g. Slemish Mountain, Co. Antrim
Volcanic Materials
Ejected during a volcanic eruption:
Lava
Acidic lava
High in silica content
Tends to be thick
Doesn’t flow too far
Gases become trapped
Violent eruptions
Volcano will have steep sides/cones
Basic lava
Low in silica content
Tends to be runny
Flows greater distances
Gases escape
Eruptions gentler
Volcano will have gently sloping sides/cones
Pyroclastic material
Volcanic ash
Rock particles known as pyroclasts or tephra
Dust
Gases
Nuée ardente
Pyroclastic flow
Volcanic gases
Carbon monoxide, steam, sulfur and hydrogen
Some are poisonous, e.g. chlorine
Predicting volcanic eruptions
Geologists forecast volcanic eruptions
The type and date of materials and distribution of deposits can give insight into volcanic activity
Tiltmeters identify bulging in the side of a volcano
If a bulge is evident, it may indicate that an eruption is imminent
Seismographs measure earthquake activity – they are positioned around the sides of a volcano
When magma begins to move it creates great heat, rocks begin to crack and break and this leads to vibrations of the Earth’s crust, which can be a clear indication of a volcanic eruption being imminent
Gases emitted from a volcano may suggest that an eruption will soon follow
Steam coming out of vents, the appearance of geysers and of hot springs also indicate possible volcanic activity
Intrusive and extrusive structures
Rocks formed within the Earth are called plutonic/intrusive rocks, e.g. granite
Extrusive structures are those formed on the surface of the Earth
Magma erupts through a crack/fissure/volcano to form extrusive rocks
Extrusive structures
Volcanoes (central vent eruptions)
Shield volcanoes
Volcanic domes
Composite volcanoes
Cinder volcanoes
Island chains
Hotspots
Fissure eruptions
Intrusive structures
Batholiths
Sills
Dykes
Laccoliths
Lopoliths
Case Study: Mount St Helens
Earthquake 18 May, 1980 at 8.32 am
Measured 5.1 on the Richter scale
Occurred directly below the northern slope of Mount St Helens
Triggered a landslide, the largest in recorded history
Travelled at speeds of 175 to 250 km/hr
Gigantic clouds of ash hovered some 16 miles above the mountain
57 human fatalities
7,000 deer, elk and bear died. Birds and other small mammals were also killed.
Elevation of the summit before the eruption was 2,950 m (9,677 feet)
Reduced by 400 m (1,314 feet) to its post-eruption elevation of 2,549 m (8,363 feet)
Case Study: The Antrim-Derry Plateau
Basalt plateau formed from volcanic activity 65 MYA
Fissures formed when the European and American plates pulled apart
Atlantic Ocean began to open, forming new continental crust
Co. Antrim was pushed further eastwards and volcanic activity ceased
The Giants Causeway is the most famous section, 60,000 hexagonal columns of basalt
Case Study: The Leinster Batholith
Pluton exposed during the Caledonian fold movement 400 MYA
Largest batholith in Britain and Ireland, 120 km from Dublin to Kilkenny
American and Eurasian plates collided, creating Leinster’s fold mountains
Dome-shaped batholith made of granite
Most overlying layers of metamorphic rock removed by denudation, only cap of resistant schist sits on top
Effects of volcanic activity
Positive
Fertile soils
Tourism
Geothermal energy
Creation of new land
Building materials
Negative
Lahars
Nuée ardentes
Loss of life
Destruction by fire
Damage to property
Effect on the environment