Elevation, earthquakes and eruptions

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History of plate tectonics, accepted since 1960s

Range of surface elevations both above and below sea level, shown on map as green/brown/beige and blue

Topography is used to desacibe the elevations on land above sea level and can be easily seen

Bathymetry is used to describe the depths and rise and fall of the rugged sea floor

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Continents

7 Major continents - Europe, Africa, Asia, Australiasia, Anatartica, North America and South America

Green shows vegetation and arid areas are coloured beige to brown (lower to higher), white shows areas in permanent ice like Greenland and Antartica

Elevation varies from low flat areas like the Great Plains of North America to rugged mountain belts of high elevation like The Alps

The Tibetian Plateau is a constant area of high elevation average of 4500 m

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Continents - continued

Parts of Death Valley in California have areas that are 100 feet below sea level

Everest in Nepal is the highest elevation at 8848 m above sea level

The lowest elevation point is at the Dead Sea on the borders of Israel and Jordan, the shores are 420 m below sea level and are encusted with salt deposits

The range of elevation across the continents is over 9 km

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Oceans

Approx 70% of the Earths surface is covered in sea water

Use of sonar to determine the elevations of the sea floor in modern day, a map showing bathymetry in hand painted in 1917. A portion of this was distributed by Nat Geo in 1968

The sea floor is very complex, more so than than the land masses

There are major areas of high elevation like thelinear submarine mountain belts like the Mid-Atlantic Ridge which rises 2 km above the deep ocean floor.

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Oceans - continued

There is a network of these ridges and they all interconnect in the all the major oceans

Some are equidistant between the land they seperate others like the East Pacific Rise is much nearer South America than Australasia

Also deep trenches, the deepest is the Marianas Trench where the ocean floor is nearly 11 km below sea level

Trenches come in two forms, they can be cresecent shaped and form alongside island chains like the Marianas Trench or can fringe the continent like one on the west coast of South America

Other trenchews include the Aleutian Arc and the Lesser Archilles Arc

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Earthquakes

Main evidence for the movement of the Earths surface

They mainly occurr along faults, like the San Andreas Fault

They are planar and exist in 2 dimensions

Seismic waves can be detected by seismometers , like ripples in a pond lose strength when they move further away from the epicentre

some measure up and down, others left to right, they are located around the globe and record activity on a seismogram

Body waves and surface waves

Body waves come in two types P Wave and S Wave

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Earthquakes - continued

P Wave is compressions and dilations, like a push travelling through a held slinky. P is the primary wave

S Wave is secondary wave, also stands for shear as the waves wiggle side to side

surface waves are the most destructive

traingulation used to identify the earthquake epicentre

magnitude is how powerful or weak the earthquake is , the greater the amplitude (height\) of the trace on the seismogram

The Lithosphere is divided into plates - plate tectonics, thicker under contintents than the oceans

Earthquakes cluster in linear belts, along the ocean ridges like the Mid-Atlantic Ridge (shallow to intermediate) and those intermediate to deep clustered along the edge of continental plates like the west coast of South America.

Earthquakes are generated when there is motion between rock masses along faults. tectonic plate boundaries

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Volcanoes

Also provide evidence of plate boundaries and give clues to the processes that occur at them

Places where molten rocks reach the surface

Can be tall and pointy or broad and less defined

One central crater or multiple vents

Range of sizes and behaviors from gently errupting to explosions

Erruptions can have global impact

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Volcanoes - continued

Outputs range from fine ash to gushing lava

Active volcanoes are found in linear belts , some of which are the same location as earthquakes

Named volcanoes include Mount Fuji, Mount St Helens, Mount Etna and Kilimanjaro

Most common location of volcanoes is on the ocean floor along the ocean ridges

Volcanoes on Hawii occur far from plate boundaries, these require further investigation

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Summary

Earths surface has a range of elevations both above and below sea level

Earthquakes mainly occur together in belts

Most volcanoes are associated with these earthquake belts and range in size, appearance and output

This information is used to define the plate boundaries

Seven major tectonic plates