Topic 1: Tectonic Processes and Hazards Flashcards
What are some points about the global distribution of tectonic hazards?
- Concentrated along tectonic plate boundries
- About 70% of all earthquakes are located around the ring of fire and 75% of volcanoes.
- The type of hazard varies by boundry
- Some earthquakes can occur within the interior of tectonic plates and volcanoes at hotspots in the middle of plates
- Over 70% of tsunamis occur in the Pacific ocean.
What are divergent plate boundries?
-Found at mid ocean ridges
- lot of shallow focus and low magnitude earthquake events.
-Most earthquakes are submarine.
- New crust is created forming mid ocean ridges in the sea and rift valleys on land. This crust is thinner and denserr than continental crust.
What are mid ocean ridges?
Ridges of underwater mountains which stretch for miles across the sea floor. Shalloe focus earthquakes occur and regular volcanic eruptions create submarine volcanoes some grow above sea level to form new islands (e.g. Iceland)
What are rift valleys?
When plates move apart on continents, crust stretchs and breaks into sets of parallel cracks(faults), the land between these faults collapse forming steep sided valleys.
What are conservative plate boundries?
2 Plates sliding past each other. No crust is created or destroyed so no volcanic activity.
Extensive shallow focus earthquakes, occasionally of a considerable magnitude. e.g San andreas fault in California.
What are convergent plate boundries?
These are actively deforming collisions with plate material melting in the mantle, causing frequent deep focus earthquakes and volcanic eruptions.
What are deep ocean trenches?
The place where the oceanic plate starts to sink beneath the continental plate.
What are fold mountains.
Mountains formed when the continental plate folds and slowly pushes upwards when they collide.
What is the benioff zone?
Where friction causes deep focus earthquakes at convergent boundries.
What are intraplate earthquakes?
Earthquakes that occur in the middle of tectonic plates. Associated with major ancient fault lines being reactivated by tectonic stresses. e.g Rhine Rift Valley. Associated with smaller magnitude earthquakes.
What are volcanic hotspots?
Volcanoes found away from tectonic plate boundries, fed by underlying mantle plumes that are hotter then surrounding mantle. The plume melts the mantle, the magma rises through cracks and erupts to form active volcanoes on the earths surface.
What is a mantle plume?
A stationary upwelling of abnormally hot rock within the mantle.
What happens as plates move over the stationary hotspot?
The volcanoes are rafted away and new ones form in their place. As oceanic volcanoes move from the hotspot they cool and subside producing older islands, atolls and seamounts. This can create chains of volanic islands, e.g hawaii.
What is the lithosphere?
The crust and the uppermost mantle
What is the asthenosphere?
Solid, plastic and partially molten laye, upper part of the mantle where convection occurs.
What is mantle convection?
Proposed in the 1930’s by Arthur Holmes. The heat derived from the radioactive decay in the earth’s core rises within the mantle to drive convection currents which in turn move the tectonic plates.
What is subduction?
The process of one plate sinking beneath the other at a convergent plate boundry.
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What is slab pull and ridge push theory?
Cold, dense oceanic plate is subducted beneath less dense continental plate; the density of the the oceanic plate pulls itself into the mantle - this is slab pull. This occurs at destructive margins.
Newly formed oceanic crust at mid-ocean ridges becomes denser and thicker as it cools. This causes it to sink under its own weight – pulling the rest of the plate down with it; this is ridge push.
What is sea floor spreading?
Occurs at divergent boundries, sea floor spread apart forming a mid ocean ridge due to a continuous input of rising magma which cools forming new land.
What is paleomagnetism?
Paleomagnetism is the study of the Earth’s ancient magnetic field as recorded in rocks, sediments, or materials, helping scientists understand tectonic plate movements and historical changes in the magnetic field.
What determines a volcanoes eruption type?
- Crystals in magma make it more viscous, so magma with a high crystal content is more likely to explode than flow.
- Gases create explosions if they cannot easily escape from viscous magma.
- High temperature magmas often erupt effusively, while low temperature magmas cannot flow easily and are more likely to erupt explosively.
Icelandic eruption.
The Icelandic type is characterized by effusions of molten basaltic lava that flow from long, parallel fissures. Such outpourings often build lava plateaus.
Hawaiian eruption.
The Hawaiian type is similar to the Icelandic variety. In this case, however, fluid lava flows from a volcano’s summit and radial fissures to form shield volcanoes, which are quite large and have gentle slopes.
Strombolian eruption.
Strombolian eruptions involve moderate bursts of expanding gases that eject clots of incandescent lava in cyclical or nearly continuous small eruptions. Because of such small frequent outbursts, Stromboli volcano, located on Stromboli Island off the northeast coast of Italy, has been called the “lighthouse of the Mediterranean.”
