Tectonics Lesson 1: Global Distribution Flashcards
Define intra-plate earthquakes
Occur in the middle or interior of tectonic plates. Much rarer than boundary earthquakes e.g. Church Stratton, Shropshire
Define volcano
Landforms that develop around a weakness in the Earth’s crust from which molten magma, volcanic rock and gases are ejected and extruded
Define seismic hazards
Generated when rocks within 700km of the Earth’s surface come under stress that they break and become displaced
Define tectonic hazards
Includes earthquakes and volcanic eruptions, as well as secondary hazards like tsunamis and represent a significant risk in some parts of the world in terms of loss of life, livelihoods and economic impact
% of earthquakes found on Pacific Ring of Fire
70%
% earthquakes found on plate boundaries
95%
Where are earthquakes distributed?
1) Oceanic fracture zone - found along mid ocean ridges
2) Continental fracture zone - found in mountain ranges
3) Scattered earthquakes in continental interiors / intra-plate earthquakes
Example of oceanic fracture zone
Mid-Atlantic Ridge
Example of continental fracture zone
Himalayas
Example of intra-plate
Church Stretton, Shropshire
How are volcanoes distributed?
Mainly along plate boundaries, but the type of plate boundary can determine whether a volcano exists
Some found away from plate boundaries in areas called hot spots
How many active volcanoes are there?
500
How many volcanoes erupt each year?
50
What determines the violence of a volcano?
Amount of dissolved gases in the magma and how easily the gases escape
What causes intra-plate earthqaukes?
1) stress building in ancient fault lines - become active again
2) fracking - stress caused by human activities - active again
What are hot spot volcanoes?
An area in the mantle from which the heat rises as a hot thermal plume from deep in the Earth
How are hot spot volcanoes formed?
Lithosphere is thinner, high heat and low pressure enables the melting of the rock.
Magma rises through the melted lithosphere and erupts as an active volcano on the surface.
Convection currents move tectonic plates over stationary hot spots, the volcanoes are rafted away, and new volcanoes form in there place over millions of years.
These volcanoes cool and subside, producing older islands, atolls and seamounts.
A chain of islands forms over time.
Example of hot spot volcanoes
Hawaiian Islands
Describe the structure of the crust
Solid
Composed of O2, Si, Al, Fe, Ca, Na, K, Mg
100km thick
200-400 C
Describe the structure of the mantle
Solid in the asthenosphere Liquid magma in the rest Composed of Si, Mg and Fe 2900km thick 84% of Earth's volume 1000-3700 C
Describe the structure of outer core
Liquid
Composed of Fe and Ni
2200km thick
4500-5500 C
Describe the structure of the core
Solid
Composed of Fe
1278km thick
4400-6000 C
