Tectonic Questions Flashcards
(21 cards)
What are the continental and oceanic crusts made up of?
Continental - SIAL (Silicon and Aluminium)
Oceanic - SIMA (Silicon and Magnesium)
How thick is the mantle?
2900km
Why isn’t direct observation of the inside of the earth just not possible?
Due to its depth and temperature
So mainly use man made blasts and seismic waves to distinguish the layers
What are convection currents?
The transfer of heat in a gas or liquid is a circular motion
Name 3 researchers and their ideas on the structure of the earth
1620 - Francis Bacon: recognised ‘easy fit’ of South Africa and South America
1692 - Edmond Halley: suggested the earth was like a Russian nesting doll, each layer habitable
1912 - Alfred Wegener: theory of continental drift
What types of evidence is there and what are the developments?
Evidence: bio, geo, climate
Developments: nuclear submarine mapping, Ewing and Tharp 1948, Harry Hess, paleomagnetism
How does the discovery of the mid-ocean trench support plate tectonic theory?
Mid ocean ridges show the earth is spreading, but it would suggest the earth is getting bigger, but trenches show that crust is also destroyed
What explains oceanic plates’ young age?
They are constantly being formed and created at mid ocean ridges and mid ocean trenches, due to their high density (3.0g/cm3)
How fast do plates move?
Plates are continuously moving relative to each other, varying between 2-16cm a year
What is a plate?
An irregularly shaped raft which floats on the asthenosphere and is succumb to convection currents below
What are a lot of earthquakes caused by?
Because the earth is neither shrinking nor expanding, if new crust is created, it must be compensated somewhere by subduction = EQ
What kind of volcanoes exist at constructive (o-o) plate boundaries?
Gentle, basic eruptions
Explain the cause of transform faults
As plates either side of the mid ocean ridge move apart, they do not do so in an uniform way, so pressure mounts and fractures the ridge, forming transform faults which are perpendicular to the plate margin below
- may widen and deepen over time
Example of submarine ridge which has become a volcano and eventually land
Surtsey Island, Iceland
N. American and Eurasian plate moving apart
Example of plates causing rift valleys
African plate and Arabian plate forming the Great African Rift Valley
If plates continue to diverge, the resulting horst and graben landscape may eventually drop below sea level, creating a new ocean
How long is the San Andrea Fault System? Where does it run through?
1300km
Cuts through most of California (6th richest economy in the world)
Which plates are the cause of the San Andreas Fault System?
Pacific plate and N American plates are slowly grinding past each other in a NW direction, forming powerful EQ
How is the San Andreas Fault System observed?
San Andreas Fault Observatory (SAFOD) makes an attempt to understand the complex system. They’ve drilled a ‘L-shaped’ hole in the fault line, filling it with thermometers, seisometers and other sensitive equipment to help monitor and understand, potentially even predicy
What are long term effects of the San Andreas Fault System?
Constant rebuilding and replanning, must avoid building on mud and sand
What kind of eruptions do destructive (o-o/o-c) plates have?
Explosive, andeisitic eruptions
Example of o-c fold mountains, ocean trench, volcano and EQ
Fold mountains: Andes
Ocean trench: Peru-Chile trench in the Pacific coast of S America
EQ: Intermediate (30-70km) and deep (30-70km)
