2.1 Earthquakes and volcanoes Flashcards
Crater def?
Depression at the top of a volcano following a volcanic eruption. It may contain a lake
Lava def?
Molten magma that has reached the Earth’s surface. It may be liquid or may have solidified
Shield volcano def?
Gently sloping volcano produced by very hot, runny lava
Cone volcano def?
Steeply sloping volcano produced by thick lava
Ash def?
Very fine-grained volcanic material
Cinders def
Small-sized rocks and coarse volcanic materials.
Magma def?
Molten rock within the Earth. When magma reaches the surface it is called lava
Magma chamber def
The reservoir of magma located deep inside the volcano
Pyroclastiques flow def
Super hot (700*c) flows of ash, pumice and steam at speeds of over 500km per hour.
Pumice def
Volcanic rock
Vent def
The channel through which volcanic material is ejected
Dormant def? (volcano)
Volcanoes which have not erupted for a very long time
Active def? (volcano)
A volcano currently showing signs of activity
Extinct def? (volcano)
A volcano which has shown no signs of volcanic activity in historic times
Intensity def?
The power of an earthquake, this is generally measured using the Richter Scale or sometimes the Mercalli scale
Richter Scale def?
An open ended scale to record magnitude of earthquakes - the higher the number on the scale, the greater the strength of the earthquake. There are more small earthquakes than large
Mercalli Scale def?
Relates ground movement to commonplace observations of, for example, light bulbs, bookcases and building damage
Epicentre def?
The point on Earths surface directly above the focus of an earthquake. The strength of the shock waves generally decrease away from the epicentre.
Focus def?
The position within the Earth where an earthquake occurs. Earthquakes may be divided into shallow-focus and deep-focus earthquakes depending on how far below the Earths surface they occur
What’s the shape of a volcano dependent on?
Type of lava
Very hot, runny lava = shield volcano
Thick material = cone volcano
Composite/cone (strato-volcanoes)
are?
Steep volcanoes
formed of viscous acidic lava, ash and cinders.
Found at Destructive plate margins
(may have more than one cone)
What are shield volcanoes?
Low-angle volcanoes
formed of runny basaltic lava
found at constructive plate margins and hotspots.
What is an earthquake?
A sudden, violent movement of the earth. It occurs after a build up of pressure causes rocks to give away
Types of crust
Continental
Oceanic
Describe Continental crust
35-70km thickness
very old, mainly over 1500 million years
Lighter, with an avarage density of 2.6
Usually made up of granite
Describe oceanic crust
6-10km thickness
younger rock, under 200 million years
Heavier with an avarage density of 3
Mainly basalt
Describe the destructive boundary process
The oceanic crust moves towards continental.
Due to oceanic being more dense it sinks beneath it, deep sea trenches and island arcs are formed
Describe the Constructive boundary process
Two plates move apart from each other; new crust is formed, creating mid-ocean ridges, volcanic activity is common
Describe the collision process from two continental crusts
Two congenital crusts collide, as neither of them sink they are folded up into mountains
describe the Conservative boundary process
Two plates move sideways past each other but land is neither destroyed nor created
What causes most earthquakes
Nuclear testing
the weight of large dams
drilling for oil/fracking
Where do most earthquake occur?
Plate boundaries
How does an Earthquake happen
Release of pressure as two plates move in different direction or at different speeds
Where do volcanoes occur
Mainly at plate boundaries however some occur in the middle of a plate, at location known as hotspots
What causes eruption
Rising magma entering a magma chamber…when pressure in the chamber is great enough eruption occurs
Primary hazards of earthquakes
Ground shaking
Surface faulting
Secondary Hazards of earthquakes
Ground failure and soil liquefaction
Landslides and rockfalls
Debris flows and mudflows
Tsunamis
impacts of earthquakes
Loss of life
loss of livelihood
Total or partial destruction of building structure
interruption of water supplies
Breakage of sewage disposal systems
Loss of public utilities such as electricity
Volcanoes direct hazards
Volcanic bombs Lava flows Ass fallout Volcanic gas Lahars (mudflows) Earthquakes
Volcano indirect hazards
Atmospheric ash fallout
Landslides
Tsunamis
Acid rainfall
Socio-economics impacts of volcanoes
Destruction of settlements Loss of life Loss of farmland + forrest’s Destruction of infrastructure Distrusting of communications Reduced tourist arrivals
Opportunity’s provided by volcanoes
Fertile soil
New land and islands for people to live on
mineral rich soil
important as tourist destinations
Case study: Soufrière Hills, Montserrat
Thé Soufrière Hills volcanoes erupted in 1995 after being dormant for nearly 400 years. Killed 19 people. Evacuation of capital city Plymouth.
Major redevelopment of housing, schools, hospitals and a new airport.
Montserrat observatory set up to monitor changes…
checks size and shape of volcano
use seidmometers to check for internal changes within crust
measure emissions of sulfur
How do you reduce impacts of earthquakes (main ways)
Better forecasting and warning
Building location
building design
emergency procedures
How can you predict and moniter earthquakes
Small-scale ground surface changes
ground tilt
change in rock stress
micro-earthquake activity (cluster of small quakes)
changed in radon gas concentration
unusual animal behaviour, especially toads
CASE STUDY: Nepal, 2015 - an earthquake in an LEDC
2015 Nepal Earthquake - magnitude 7.8 - 25tg April as a result of the indian plate colliding with the Eurasian plate.
Epicentre of the earthquake was 80km north of Capital, shallow focus of 15km.
Occurred around midday
9k deaths in main earthquake and 200 were killed in an aftershock of 7.3
Fatalities were less in rural parts as less buildings.
Economic cost of 7billion dollars - 35% of Nepals GDP. Asian development bank provided 3 million grant for emergency relief, including shelter, food, blankets and cooking utensils
