Dynamic Landscapes Tectonic Processes & Hazards

Flashcards about tectonic processes and hazards.

Plate tectonics

Scientific theory explaining the movement of the earth’s crust, resulting in geological events such as seismicity, volcanism, continental drift, and mountain building

Examples of major tectonic plates

North American and African plates

Example of a minor tectonic plate

Cocos plate off the west coast of Central America

Sunda plate

Extends from the northern tip of the Indonesian island of Sumatra to the western tip of Papua New Guinea

Four main types of plate boundary

Constructive (divergent), Destructive (Convergent), Collision (continental to continental), Transform (conservative)

Intraplate earthquakes

The result of ancient fault lines; small movements along these old faults build up friction and strain over time which is eventually released causing low magnitude earthquakes

Hotspots

Associated with mantle plumes and the upwelling of hot molten material from deep within the earth’s mantle

Examples of hotspots

Hawaii and Nyiragongo

Isostatic readjustment

Ice is removed from the surface after an ice age; crust readjusts up or down which can trigger earthquakes

Human activity

Can trigger earthquakes such as fracking

Lithosphere

The upper mantle is more brittle and welded to the overlying crust.

Asthenosphere

Mantle below the lithosphere; despite being solid it flows slowly as a result from heat from below and convection currents

Mesosphere

Part of the Earth's mantle below the asthenosphere, but above the outer core

Outer core

Mostly liquid iron; only allows p waves to pass through

Inner core

Solid nickel and iron

Convection

Created from the heat radiating out from the radioactivity in the inner core

Sea Floor Spreading

Material rises to form new crust, this creates push at the ocean ridges which will lead to movement

Slab Pull

At subduction zones along convergent boundaries denser oceanic plates sink to create slab pull

Plate Margins

The area adjacent to plate boundaries that are affected by the movement

Alexander Von Humboldt

German geographer who wrote about the apparent fit between the north east of South America and the west coast of Africa as early as 1801

Alfred Wegener Theory of Continental Drift (1912)

Used evidence to suggest that a supercontinent existed up to 250 million years ago, he named it Pangaea

Pangaea split in two to form…

Laurasia (northern continent) and Gondwanaland (southern continent)

Arthur Holmes (1919)

He suggested that the continents were carried by flow of the mantle on which they sat, and that the mantle was flowing because it was convecting

The National Geographic Society (1947)

Commissioned Maurice Ewing to explore the mysterious ridge which had been discovered in the middle of the Atlantic Ocean

Maurice Ewing's findings

Young and thin ocean crust was made of volcanic basalt and not sunken continental material

Bruce Heezen and Marie Tharp

Produced 3D maps of the North Atlantic Ocean using sonar and earthquake data

Harry Hess & Robert Dietz (1960)

Proposed the theory of sea-floor spreading

J. Tuzo Wilson (1965)

Proposed that plates might move over fixed ‘hotspots’ in the mantle, forming volcanic island chains like Hawaii

Drummond Matthews & Fred Vine (1963)

Studied the ancient magnetic fields on the ocean floor, found that as new rocks form at the ridge, the magnetic minerals within the rock align themselves in the direction of the magnetic field at the time

Third type of plate boundary - transform faults

Transform faults slip horizontally, allowing plates to slide past each other without any oceanic crust being created or destroyed

GPS (1983)

Measurements on land can be made within centimetres, giving precise information about the changes to Earth’s surface

Accretionary Wedge (prism)

A zone of deformed sediment made up of thrust slices scraped off a subducting oceanic plate and added onto the overriding plate

Batholiths

Large areas of intrusive (usually granitic) rock typically associated with subduction zones or hot spots

Example of Oceanic-Continental plate margins

Nazca/South American plate

Subduction

Oceanic plate is forced under the continental plate

Ocean trenches

Long, narrow depressions with depths of 6000-11000m

Benioff Zone

Releases vast amounts of energy in the form of earthquakes which are felt on the surface

Collision Zones -Continental To Continental Plate Boundary

Sediments and rocks from the former ocean floor are forced upwards to form the fold mountains of the Himalayas

Mid Atlantic Ridge (MAR)

North and South American plates are being pulled apart from the Eurasian and African Plates by convection cells

Graben

The central portion of the rift sinks leaving behind a rift valley on the ocean ridge

Horst

Upstanding blocks

Hydrothermal Vents

Water seeps through cracks in the seafloor and is heated by molten rock deep below the ocean crust

Continental Rifting - Great Rift Valley East Africa

Plates move apart in continental crust

Transform (Conservative) Plate Boundary - The San Andreas Fault

Pacific Plate is moving faster than the North American Plate (30mm and 50mm per year)

Earthquakes occur…

Friction between plates at these margins causes pressure and tension to build up, when this is released, it causes rocks to fracture along faults and the energy released generates seismic waves

Focus of an earthquake

The point at which the strain and pressure is released

Epicentre

The point on the earth’s surface directly above the focus

P Wave

Fastest kind of seismic wave and is the first to 'arrive' at a seismic station; can move through solid rock and fluids

S Waves (secondary or shear waves)

Slower than a P wave and can only move through solid rock, not through any liquid medium

Rayleigh Wave

Only travels through the surface of the crust; produces a rolling motion that moves the ground up and down and side to side

Love Wave (surface waves)

Fastest surface wave; only travels through the surface of the crust; moves side to side as it moves in a forwards direction

Seismometer

Measure seismic waves

Shadow Zone

Area of the Earth's surface where seismographs cannot detect an earthquake after the waves have passed through the earth

Crustal fracturing

The result of the energy released during an earthquake which causes the earth’s crust to crack

Aftershocks

When the earth readjusts along the faultline after the main earthquake event

Liquefaction

Takes place when loosely packed, waterlogged sediments at or near the ground surface lose their strength in response to strong ground shaking

Tsunamis

A series of larger than normal waves caused by submarine earthquakes at subduction zones

The earthquake that generated the tsunami in the Indian ocean in 2004 was the result of…

Subduction of the Indian plate under the Sunda plate and the Burma microplate

Subduction is not a smooth process…

The friction between the subducting plate and the overriding Burma plate leads to pressure and stress building up over time

Megathrust

Fault moved vertically 20 metres and horizontally over 400km, displacing a huge column of water that sent a series of waves radiating outwards towards the coastlines

Volcanoes

At convergent boundaries where subduction takes place, magma rises and melts the overlying plate

Lava Flows

Streams of magma that have erupted onto the earth’s surface; extremely hot, reaching temperatures upto 1170 degrees celsius

Pyroclastic Flows

Contain a high-density mix of hot lava blocks, pumice, and volcanic gas; extreme temperatures are generally between 200°C and 700°C

Tephra

Pieces of volcanic rock that ejected from a volcano

Cinders

Sand sized fragments

Lahars

Mudflows with the consistency of wet concrete; snow and ice on volcanic summits melt during eruptions and flow down the flanks of the volcano

Jokulhaups

Volcanic eruptions beneath an ice field or glacier cause rapid melting

Phreatic Eruptions

Water, such as groundwater, seeped into the volcano and got superheated by magma and flashed to steam