Types of volcano
Dome- destructive, Rhyolitic or Andesitic, steep sides due to high viscosity lava that flows a short way
Caldrea- Destructive, Rhyolitic or Andesidic, High viscous lava, wide circular crater several Km across
Composite- Destructive, Rhyolitic or Andesidic, layers of ash and sinders
Shield- Constructive or hotspot, Basaltic, gently sloping sides due to low viscosity lava which flows for long distances
Fissure- Constructive, Basaltic, flat surface due to low viscosity lava which flows for long distances, long liniar vent, few M wide but several Km long.
Intrusive volcanic activity
Dykes - Where the magama has flowed into gaps in the surrounding rock and cooled (cusing cooling cracks horizontially), it has formed vertical dykes
Sills- Sills where magma flows horizontially between layers of rock (cooling cracks form vertically)
Batholiths- Large chamber of magma cool underground and form domes of igneous rock
Hot springs- ground water emerges at surface, close to areas of intrusive volcanic activity, temp varies from 20 degrees toover 90 degrees, often high mineral content as hot water can contain a lot of dissolved solids.
Geysers- type of hot spring where hot water and steam are ejected from the surface, form in areas of intensive volcanic activity. eg Strokkur geyser in Iceland. Ground water is heated to above boiling by magma deep within the crust, hot water is pressurised and forces way to surface through cracks in rocks. erupt periodically, as only a result of high pressure.
Extrusive activity continued
Boiling mud pools- Another type of hot spring found in areas with very fine granualated soil e.g. soil rich in volcanic ash. Hot spring water mixes with soil to form a hot muddy pool.
Brightly coloured mud is found here due to soil rich in minerals e.g. yellow stone
Hot spots- Occur away from plate margins caused by magama plmes rising from the mantle, volcanoes form above magma plumes. The crust moves above the plume and new volcanoes form as hotspots remain stationary, creating a chain of volcanoes e.g. Hawaiian islands
Caused by built up tension at all 3 plate margins, when pressure is released the plates suddenly jerk past eachother causing seismic waves to jolt the surface.
Focus is below the surface (lithosphere) where waves spread out from. Doesnt have to be a single point, for example could be along the fault line. Waves are stronger and can cause more damage near the focus.
Epicentre on the surface of the earth, where EQ is felt first. point on the surface closest to the focus.
- Reactivation of old fault lines
- Subsidence (ground sinks)
- Pressure on surface rocks from water in large reservoirs.
Structure collapse, tsunamis, avalanches, landslides or liquefication.
Three main types of seismic wave are:
Primary (P waves)-
- Fastest type of wave
- Can travel through solids and liquids
- Push and pull earth in same direction as wave is travelling
Secondary (S waves)-
- Have a shearing effect and cause a lot of damage
- Only travel through solids
- Waves move at 90 degrees to the direction of travel (up and down)
- Slower than P and S waves
- Love waves only travel through solids, move surface side to side & cause a lot of damage
- Rayleigh waves can travel through liquids and solids (a rolling motion like the sea)
Seismometres- measure energy relase by an EQ.
- Records can determine frequency
Scales to measure EQ's:
- Logarithmic scale (eg. magnitude 5= 10x stronger than magnitude 4).
- Each value on the scale represents 30X more energy released compared with before.
- Major EQ are magnitude 7
- No limit on how high the scale goes but biggest on record is 9.5 in Chilie 1960.
Mercalli- Measures the severity of impacts
- observations of the events eg photographs and reports
- 1= only instruments feel and 12=total destruction
Tsunamis are large waves caused by dsplacement of large volumes of water
- Underwater earthquakes- Sea bed moves, displaces water, waves to radiate from epicentre
- Volcanic eruption and landslides- Can slide into the sea and displace water
- More powerful when close to the coast
- Tsunamis lose energy as they travel towards land
- Waves travel very fast in deep water and can hit shore without much warning= high deaths
- In open ocean they travel at between 500-950kmh with long wavelength (200km), small amplitude (1m)
- Closer to land (shallower water) waves compress together & energy becomes more concentrated so slow down to less than 80kmh with a short wavelength (20km) but high amplitude (many M).
Managing the impacts of Earthquakes
A hazard is a threat posed to either people and/or their property
Prediction- Impossible to predict but clues are:
- Small tremors
- Cracks in rocks
- Strange animal behaviour
Techniques can be used to aid prediction:
- Warning systems e.g. seismometers detecting p waves which arrive before destructive s waves
- Using past records
Protection- Impact reduced through planning measures such as:
- Specifically designed EQ resistant buildings e.g. cross bar reinforced and pendulum buildings
- Construction laws to prevent building in Eathquake prone areas
Managing the impacts of Volcanic hazards
Prediction- Can be roughly predicted
Signs of an eruption are:
- Small EQ's
- Change in shape
- Buldges in surrounding land where magma has built up
- Re-enforced buildings to protect from falling ash and debris
- Divert lava using barriers, however can be unpredictable eg mount st helens exploeded from the side. and barrier only effective with slow moving lava.
Managing the impacts of Tsunamis
- EQ's detectable before the disaster and are warning centres all around the world
- Give time for evacuation, however they require good communication systems and adequete time to escape.
- Raised buildings with open foundations
- Concrete foundations are less likeley damaged
- Tsunami walls
Managing the impacts of Hazards- Planning and Educ
Planning and education- Processes can be cost effective
1. Do not build on areas that are in a hazrdous location
2. Emergency services can train and prepare for disasters e.g. FEMA
3. Governments can plan evacuation routes for people to follow in case of emergency
4. Governements can plan lessons to teach people how to avoid danger in case of an emergency
5. All these methods are cost effective
Factors that increase severety of impacts-Developm
Development level of a country can influecnce impacts:
Higher in LEDCs becasue:
- No money for preparation or response
- Buildings poor quality
- Infrasructure is worse so emergency aid cant reac affected areas
- Healthcare not so good so cant treat people
- Dependant on agriculture which is damaged by eruptions or tsunamis
MEDCs have higher economic impact as buildings are worth more.
Factors that increase severity of impacts-Populati
Population is worse affected when densley populated due to:
- Collapsing build ings in densley populated areas
- Hard to evacuate large numbers of people with limited routes
Timing impacts can be worse:
- Time of year (if in winter people exposed to elements)
- Time of day (if at night many people sleeping and may be killed or trapped)