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Extrusive Volcanism: Associated Hazards and Their Management - Coggle…
Extrusive Volcanism: Associated Hazards and Their Management
occurs when magma reaches the earth's surface and causes volcanic eruptions, leading to the formation of various volcanic features
Structures of a typical volcano
Magma chamber
a large space within the lithosphere in which magma, rising from a deeper level, accumulates until it rises to the surface at the site of a volcano
Vent
an opening in the crust through which volcanic material flows
Crater
Circular depression at the top of the top of the volcano
Main vent
Secondary vent
alternate layers of lava and pyroclast
Location of Occurrence
Occurs most at convergent plate margins at subduction zones
occurs at divergent plate margins too
mainly occurs along mid-ocean ridges where the crust is separating
mantle hotspots
most notable ones include the Hawaiian Islands, which lie in the middle of the Pacific Plate
most of the eruptions occur around the Pacific Ring of Fire
Volcanic Hazards
Lava flow
Basaltic magma (less viscous magma)
aa flow
pahoehoe flow
Mudflow
Pyroclastic flow
formed when hot, incandescent gases are combined with pyroclasts
cloud of ash and gas
Ash fall
Tsunami
Types of volcanic eruptions and landforms
shield volcanoes
common in oceanic areas
built primarily by the successive flows of basaltic lava from non-explosive eruptions and usually contain only a small percentage of pyroclastic material
convex slopes and are dome-shaped
slopes are gentler near the summit as the lava is hot and fluid and will readily run down a gentle slope
increasing slope angle with increasing distance from the summit
has a wide base
stratovolcanoes/composite volcanoes
mostly lie above subduction zones at the Pacific Ring of Fire
produced when more viscous lavas of andesitic composition are extruded and represent the most violent type of volcanic activity
built of inter-bedded lavas and pyroclastic material
concave slopes where the summits are steeper than the base
a significant proportion of it is made of lahars
caldera
the summit have nearly circular depressions that exceed one kilometer in diameter
most are thought to form when the summit of a volcanic structure collapses into the partially emptied magma chamber
Managing Volcanoes
Predicting Volcanic Eruptions
Seismic Activity Monitoring
Gas Analysis
Hazard Mitigation
Lava flow diversion
example: On the Icelandic island of Heimay
Protection against pyroclastic flow
build a series of barriers designed to channel the energy of a flow upwards and so encourage it to form a buoyant plume
Lahar protection
mudflows supplied by ashfall on steep slopes can be diverted by pre-dug channels and held back by dams to trap the larger material and reduce the volume e.g. sabo dams
Hazard Maps
making the authorities and locals aware of the hazards and the appropriate responses in each location, and enforce planning regulations to prevent building in the most hazardous places, making modifications to roofs and protecting crops
Response to volcanic eruptions