Tectonic Processes and Hazards Flashcards
What are Intra-Plate Earthquakes?
These occur in the middle or interior of tectonic plates and are much rarer than boundary earthquake. Scientists think that they occur when stress builds up in ancient faults -> causing them to become active again.
They are harder to predict as they don’t occur in well-defined patters.
What are Volcanic Hazards?
Associated with eruption events.
What is a Volcano?
A landform that develop around a weakness in the Earth’s crust from which molten magma, volcanic rock and gases are ejected and extruded.
What are Seismic Hazards?
Generated when rocks within 700km of the Earth’s crust surface come under such stress that they break and become displaced.
What are Tectonic Hazards?
These include earthquakes and volcanic eruptions as well as secondary hazards such as tsunamis and represent a significant risk in some parts of the world in terms of loss of life, livelihoods and economic impact.
What Percentage of earthquakes are found along Plate Boundaries?
95%
What Percentage of earthquakes are found in the Pacific Ring of Fire?
70%
What is the Oceanic Fracture Zone (OFZ)?
Activity found in mid-ocean ranges e.g. the mid-atlantic ridge.
What is the Continental Fracture Zone (CFZ)?
Activity found in mountain ranges e.g. across the himalayas.
What are earthquakes Scattered in Continental Interiors?
Found along fault lines e.g. the Church Stretton Fault in Shropshire.
How many Active Volcanoes are there Globally?
Around 500
How many Volcanoes Erupt each year?
50
Where can Volcanoes form?
-Majority on plate boundaries -> the type of plate boundary can determine whether a volcano exists and what type it is.
-Some on Hotspots.
What is a Volcanic Hotspot?
An area in the mantle from which heat rises as a hot plume from deep within the earth, often called a ‘mantle-plume’.
High heat and low pressure at the base of the lithosphere enable melting of the rock.
What is Sea Floor Spreading?
-This is the process of new crust pushing tectonic plates apart.
-In the middle of many oceans there are mid-ocean ranges or under water ranges, formed when magma is forced up from the asthenosphere and hardens forming new ocean crust.
What is Subduction?
The process of a plate being destroyed as two oceanic plates or an oceanic and continental plate move towards each other, one slides under the other into the mantle, where it melts into an area called the Subduction Zone.
What is Slab Pull?
Newly formed oceanic crust at mid-ocean ridges becomes denser and thicker as it cools -> this causes it to sink into mantle under its own weight - pulling the rest of the plate down with it.
What is Mantle Convection?
Heat produced by the decay of radioactive elements in the earth’s core heats the lower mantle -> Creating convection currents.
-These hot, liquid magma currents ae thought to move in circles in the asthenosphere - thus causing the plates to move.
What is Palaeomagnetism?
-In the 1950s, studies of palaeomagnetism confirmed that sea floor was spreading. Every 400,000 years or so, the earth’s magnetic fields change direction i.e. the magnetic north and south pole.
-When lava cools and becomes rock, minerals inside the rock line up with the earth’s magnetic direction (polarity) at the time.
What is the Earth’s Crust?
-It is made of Oxygen, Silicon, Aluminium, Iron, Calcium, Sodium, Potassium and Magnesium.
-Beneath continents the earth’s crust can be 30-70 km and under oceans it is 5-7 km.
-The crust is solid and is 1000°c at the base.
What is the Lithosphere?
-It is made of rocks and minerals.
-The lithosphere includes the crust and the upper mantle so it’s about 100-300 km.
-The lithosphere is solid and is 300-500°c including the crust and upper mantle.
What is the Asthenosphere?
-It is the section of the mantle directly underneath the lithosphere.
-It is made of periodtite which is a rock containing mostly minerals olivine and pyroxene.
-It is about 200 km thick.
-It is solid that can behave like liquid and is 1,500°c.
What is the Mantle?
-It is made of mostly Iron, Magnesium, and Silicon.
-It is 3000 km thick, making it the thickest layer.
-It is a dense, semi-solid layer with temperatures of 1,000°c to 3,700°c.
What is the Outer Core?
-It is made of Iron and Nickle.
-It is about 2,200 km thick.
-It is liquid and ranges from 4,500-5,000°c
-It is mainly heated by radioactive decay of the element Uranium and Thorium which churns turbulent currents. This generates electrical currents which generate earth’s magnetic field.
