Different types of volcanoes:
Super Volcanoes:
Volcanoes that erupt over 1,000km3 of material in a single event. Yellowstone super-volcano
in Wyoming, caldera 75km in diameter.
Hot Spots:
Basaltic Lava
Constructive Margins
Lower viscosity, hotter (1200 degrees) and cools slower
Frequent but relatively gentle eruptions of lava and steam → effusive
Lower silica content
Fissure
E.g = Heimaey, Iceland
Eurasian and N.American plates
Form around spreading ridges and rifts
Occur where an elongated crack/open fissure
allows lava to spill out.
Shield
E.g = Mauna Lau, Hawaii
10,000m above sea-floor
Occur on hot spots
Gently sloping cones of less viscous lava
An area of intense volcanic activity where a mantle plume erupts, located away from plate
boundaries.
• As basaltic shield volcanoes erupt through drifting ocean crust, they may build up to
form an island.
• If they become part of the plate they are gradually moved away from heat source.
• Some islands will become eroded by waves and form flat-topped sea mounts
(guyots).
• Plate moving quickly in one direction creates a sequence (Hawaiian Chain).
• Plate rotating slowly creates a cluster (Canary Islands).
E.g = Hawaiian Islands
Middle of Pacific Ocean, over 3200km from nearest plate boundary. Includes Hawaii, Maui,
O’ahu, etc…
Volcanic Explosivity Index (VEI):
Measure of eruptions by combining magnitude and intensity on logarithmic scale form 0-8
(most). Explosivity includes volume, height ejected, duration, etc…
Volcanic eruptions generate distinctive hazards:
Hazards generated by volcanic eruptions:
Lava flows – Streams of molten rock from an erupting event. Speed depends on viscosity
and ground steepness, though all burns and buries infrastructure, property, natural
vegetation and agricultural land.
Pyroclastic flows – Hot gas, ash and rock travelling at high speed (100km/h and over 500
degrees). Inhalation causes death.
Tephra – Material ejected from volcano.
Toxic Gases – CO, CO2, SO2, Acid rain produced.
Lahars – Mud flows of melted snow, rock, ash and soil (50km/h). Southeast Asia’s ash
covered volcanic slopes generate lahars after heavy rain.
Floods – Eruptions below ice fields cause rapid melting and meltwater escapes as a torrent
of water. Iceland volcanoes under Vatnajökull ice field.
Tsunamis – Eruptions on island volcanoes, waves at 600km/h. Krakatoa, 1833 drowned
36000 people.