Physical geo presentation for volcanoes
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Transcript of Physical geo presentation for volcanoes
GLOBAL DISTRIBUTION OF TECTONIC HAZARDS
Tectonic hazards include:Seismic activity (earthquakes)
TsunamiVolcanoes
EARTHQUAKES
Most earthquakes occur in clearly defined linear patterns which generally follow plate boundaries
Why?
THE MID-ATLANTIC RIDGE There is a clear line of earthquakes
associated with the Mid-Atlantic Ridge This is because of the build up of pressure in
the Earth’s crust as magma escapes from the volcano(explanation)
There is a broader line of earthquakes along the west coast of America and the Eastern Pacific associated with the subduction of the Nazca Plate beneath the South American Plate – a destructive plate margin
EARTHQUAKES
Broad belts of earthquakes are associated with : 1. Subduction (example) and
(explanation)2. Collision margins e.g in the Himalayas
(explanation)
EARTHQUAKES
Narrow belts are associated with : 1. Constructive margins (example and
explanation)2. Conservative margins e.g in California’s San
Andreas Fault line(example and explanation)
NB: Note that 100km wide can be classified as NARROW
EARTHQUAKES
There are also isolated occurrences of earthquakes that may be due to:
HUMAN ACTIVITIES
or
HOTSPOTS
HUMAN ACTIVITIES
HOTSPOTS
VOLCANOES
WHERE ARE VOLCANOES FOUND?
WHERE?Most volcanoes are found along plate boundaries although some volcanoes are found on hotspots e.g volcanoes of Hawaii
About ¾ of the Earth’s 550 historically active volcanoes lie along the Pacific Ring of Fire
This includes many of the world’s most recent volcanoes e.g Mt. St. Helens, USA and Mt. Unzen, Japan
WHERE?
Other areas of vulcanicity include:IcelandMontserrat in the CarribeanMt. Nyiragongo in the DRC
And some submarine volcanoes e.gKick ‘emJenny, off Grenada in the Carribean
WHERE?Volcanoes are found along the plate boundaries of major plates
Although the deeper levels of the Earth’s crust are much hotter than the surface, the rock is usually not molten because of high pressure
However, along plate boundaries, there is molten rock, magma, which supplies the volcanoes
WHERE?Most of the world’s volcanoes are found in the Pacific Ring of Fire
These are related to the subduction beneath either continental or oceanic crust
Subduction in the oceans produces island arcs, such as the Aleutian Islands, formed by the Pacific Plate subducting beneath the North American Plate
WHERE?
Subduction of oceanic crust beneath the continental crust, results in formation of young fold mountains e.g The Andes, have been formed where the Nazca Plate subducts beneath the North American Plate (map showing this)
HOTSPOTS
HOTSPOTSHOTSPOT: A jet of hot material
rising from deep within the mantleNot all volcanoes are found along
plate margins Those in Hawaii are found in the
middle of the oceanThe Hawaiian islands are a line of
increasingly older volcanic islands which stretch north-west across the Pacific Ocean
These volcanoes are related to the movement of a plates above the hot fluid mantle
HOTSPOTS
Hotspots can be found beneath continents e.g The East African Rift Valley
These hotspots can:Produce volcanoesBreak up continents and form
new OCEANS
CONTRASTING VOLCANOES AT DIFFERENT PLATE MARGINS
Viscous lava (composition)
Erupt explosively (gases)
Relatively fluid lava (composition)
Erupt less explosively (gases)
SUBDUCTION ZONE MID-OCEAN RIDGES
THE TYPE OF MAGMA
VISCOUS FLUID
CONTRASTING VOLCANOES AT DIFFERENT PLATE MARGINS
Slab of the oceanic plate warms up slowly as it slides down the subduction zone. Volatile compounds such as carbon dioxide and water leave the slab and rise to the mantle so that it melts. Magma is then able to rise
Hot fluid rock rises up due to convection currents and the upper mantle begins to melt causing eruption of basaltic lava
SUBDUCTION ZONE MID-OCEAN RIDGES
HOW BIG AND HOW VIOLENT WILL THE EXPLOSION BE?Huge explosions occur whenever
water meets hot rock because water vaporises increasing pressure until the rock explodes
The likelihood of a huge eruption depends largely on the viscosity of magma and hence, its composition
Gases dissolve quite easily in molten rock underground because there are very high pressures there
However, as magma rises to the surface the pressure drops and some of the gas may become insoluble and form bubbles
STYLE OF ERUPTIONProcesses occurring at different plate margins determine the style of eruption
These processes produce different, but predictable compositions
Some minerals melt before others in Partial Melting which alters the composition of the molten rock produced
PARTIAL MELTING
PARTIAL MELTINGPartial melting of the Earth’s
mantle produces BASALT.At subduction zones, the older and deeper slabs experience greater partial melting and this produces a silica-rich magma
REFERENCESGeography (Guiness and Nagle)http://earthquake.
usgs.gov/learn/topics/plate_tectonics/rift_man.php
http://geology.com/volcanoes/types-of-volcanic-eruptions/
Mauna Loa, Hawaii
DONE BY:VIMBIKAYI CHIMUKA