Hazardous Earth Flashcards
What are the 3 main parts that make up Earth?
Core, mantle and crust.
What is the asthenosphere?
The semi-molten layer that forms the top part of the mantle.
What is the lithosphere?
The layer found between the crust and asthenosphere that breaks up into tectonic plates.
What separates the mantle and crust?
the Mohorovičić discontinuity, also known as ‘Moho’.
The 2 types of plates are called…
Continental and oceanic.
Properties of oceanic crust?
Thin, made from basalt, density - 3.0kg/m3, SIMA.
Properties of continental crust?
Thick, made from granite, density - 2.6-2.7kg/m3, SIAL.
The 3 theories for tectonic plate movement?
Convection currents, slab PULL & ridge PUSH.
Why is continental fit weak evidence for continental drift?
Coasts of continents have been exposed to geomorphological processes (eg. erosion).
What is palaeomagnetism?
The idea that the magnetic poles switch and metal minerals in rocks change alignment - magma will cool in the direction of the magnetic north pole.
What happens at the 3 different plate boundaries?
Convergent - collide.
Divergent - move away.
Conservative - slide past each other.
What happens at convection currents?
Decay in core heats mantle, magma rises and spread to asthenosphere and sinks = friction in crust.
What happens during ridge push?
Magma rises through the crust, cools and forms underwater. Dense mountains slide away from each other (gravity).
What happens during slab pull?
Oceanic plate subducts into hot mantle due to gravity.
The 3 different plate boundaries found at convergent plate boundaries…
Oceanic-continental = fold mountains
Oceanic-oceanic = island arcs
Continental-continental = mountains
What are the 2 categories of eruptions?
Explosive and effusive.
Features of composite/strata volcanoes…
Found mainly at convergent plate boundaries.
Steep.
Explosive eruptions.
Have long periods of inactivity.
Erupt gases, ash, lava bombs.
Acidic lava type of rhyolite and andesite.
55% SiO2 (silica) - more viscous.
Features of shield volcanoes…
Found mainly at divergent plate boundaries.
Shallow.
Effusive eruptions.
More frequent eruptions that last for longer periods.
Erupt gases and lava flows.
Runny lava type of basalt.
45% SiO2 (silica) - less viscous.
The six types of volcanic eruptions…
Icelandic (the least violent), Hawaiian, Strombolian, Vulcanian, Vesuvian, Plinian (the most violent).
The seven hazards that can be caused by volcanic eruptions…
Lava Flows, Pyroclastic Flows, Tephra, Tsunamis, Toxic Gases, Lahars, Flooding.
Why do volcanoes erupt?
As magma collects within the magma chamber, pressure increases and causes fractures, where the magma will be released through a volcanic eruption.
How has the Hawaiian chain of islands been formed?
Formed at a hotspot. Basalt accumulation on the ocean floor caused the islands to move from the hotspot and become extinct.
What is VEI and how is it calculated?
Volcanic Explositivity Index - calculated using magnitude and intensity (can only be used for explosive volcanoes).
What are earthquakes?
A release of stress that has built up in the Earth’s crust due to tension, compression, shearing of rocks.
Where is the epicentre?
Above the earthquake focus at the Earth’s surface.
Where are earthquakes mostly concentrated?
Mid-ocean ridges, ocean trenches/island arcs, collision zones, conservative plate boundaries.
Features of a P (primary) wave…
Fast-travelling.
Low frequency.
Vibrate in the direction of travel.
Travel through Earth’s interior (solids + liquids).
Cause least amount of damage.
Features of a S (secondary) wave…
1/2 of P-wave speed.
High frequency.
Vibrates at right angles to direction of travel.
Can’t pass through liquids.
Features of a L (love/surface) wave…
Slowest.
Low frequency.
Rolling vertical movement and right angles to direction of movement.
Displaces crust.
Travel through outer crust only.
Features of a deep focus earthquake…
70-700 km deep.
Extremely high temperatures.
Minerals change type and volume of deep focus.
Occur at subduction zones, and are measured on Moment Magnitude Scale.
Features of a shallow focus earthquake…
Around 70 km.
Occur in cold, brittle rocks from fractured rocks and stress of crust.
Release low levels of energy.
Pro and con of Richter Scale…
+ Has no upper limit and represents 30-fold increase in release of energy.
- Doesn’t show impacts on people and can’t express physical movement of the crust.
Pro and con of Modified Mercalli Scale…
+ Qualitative assessment, based on observation/description.
- Damage caused may not represent the earthquake’s overall strength. Many people will have different opinions of the destruction that occurred.
Pro and con of Moment Magnitude Scale…
+ Uses physical movement and energy equivalents.
- Can’t be used to measure small earthquakes.
The four hazards that can be caused by earthquakes…
Groundshaking, Liquefaction, Landslides/Avalanches, Tsunamis.
What is ‘modifying the event?’
Mitigating hazards generated from the tectonic activities.
What is ‘modifying vulnerability?’
Reducing how vulnerable people are when exposed to a tectonic event.
What is ‘modifying loss?’
Reducing loss of life and damage to properties after the tectonic event.
