Hazardous Earth Flashcards
What are the layers of the core and their properties ?
Inner core - solid iron (5000°-7000°)
Outer core - semi molten and a liquid of iron and nickel ( 4500°-6000°)
What are the layers of the mantle?
Asthenosphere- upper part of the mantle on which the plates float
Lower mantle - thickest layer (2900km)
What are the parts of the lithosphere (crust)?
Continental crust - older, thicker, made of granite and is less dense ( 45-50km). It makes up our landmasses.
Oceanus crust - younger, thinner crust ( 6-10km) and very dense. It is made of basalt and lines the ocean floor.
What is plate tectonics?
The theory that huge slabs of irregular shaped rocks on the earths surface form to make jigsaw like system that moves the lithosphere over the asthenosphere. It provides the foundation for continents and oceans.
What is the idea of how plate tectonics have change and what is the proof?
250 million years ago, the continents were joined together in a supercontinent called Pangea. Since then, the continents have been moved by a process called continental drift. This is due to convection currents created by the immense heat in the inner core. Fossil correlations found on either side of the oceans, rock and mountain correlation meaning identical rock structures are found on different sides of oceans suggesting they were once joined.
What moves the plates?
Convection currents contribute to plate movement as the intense heat in the core heats the magma creating a convection current. The mantle then rises the the earths crust but then follows a circular movement either way to then flow back to the core to be reheated at the trenches.
What are the plate margins and what happens at each one?
Divergent plate margins - plates move away from each other
Conservative plate margins - plates slide past each other at different speeds
Convergent plate margins - plates move towards each other.
What happens at a conservative plate margin and name an example?
( San Andreas fault)At a conservative plate margin plates slide past each other or in the same direction at different speeds. As the plates move past each other they become locked but are still trying to move so friction and pressure builds up. When the pressure is suddenly releases it creates immense seismic activity and sends shockwaves through the crust causing an earthquake. Earthquakes at conservative plate margins tend to be intense as the focus is close to the surface. Not volcanos occur at this margin. The focus is where the original sliding ands shaking occurs and the epicentre is the point of the most shaking on the the surface
What happens at a convergent plate margin and name an example?
At this margin plates move towards each other, this collision process is called subduction. As a continental plate and oceanic plate move towards each other the oceanic plate is subducted beneath the continental plate as it is denser. As the plate sinks into the mantle it starts to melt meaning magma begins to fill up the cracks and erupt through a volcano. This volcanos tend to be composite so are explosive. If two continental plates converge they can collide and cause new land to form Earthquakes can also occur. ( Himalayas or ring of fire )
What happens at a divergent plate margin, name an example?
At a divergent plate margin plates pull apart from each other. As the crust breaks magma fills up the gap and makes new land. At these margins there tends to be shield volcanos. ( mid Atlantic ridge)
What is another way of creating a volcano?
Hot spots( points at which magma forced its way through the middle of a plate). Due to convection currents heat beckons to facilitate the melting of the rock at the bottom of the lithosphere. Where the brittle upper portion of the mantle meets the crust, magma often pushes through the cracks in the surface to form volcanos.
What are composite volcanos ?
Composite volcanos are found on a convergent plate margin and are steep sided and cone shaped made up of lava and ash layers. (Their eruptions tend to consist of pyroclastic flows rather then lava flows.) Their eruptions are highly explosive and very destructive. The lava is very viscous and has andesitic lava which contains lots of silica and gas but isn’t very hot.
What is a shield volcano?
Shield volcanos are found on a divergent plate margin and are formed of not very viscous, runny lava that flows a long way before solidifying. Shield volcanos have gently sloping sides and a wide base. They contain basaltic lava which is very hot but doesn’t contain much silica or gas.
What type of volcano is more dangerous?
A composite volcano is more dangerous as it is more explosive. This is due to its andesitic lava which is more viscous and contains lots of silica. As a result this traps gases which builds up pressure leading to a sudden explosion ph hot gases and ash ( pyroclastic flow). Shield volcanos are more effusive and less violent so are less destructive.
What is a Supervolcano?
A volcano but on a massive scale. This means effects and danger is magnified.
What are the properties of a composite volcano?
Pyroclastic flow, lava layer, main vent, crater, conelet, dyte, Ash layer and a magma chamber
What are the properties of a shield volcano?
Main vent, solid lava layer, magma chamber
What is a primary hazard?
Primary hazards are caused but the initial eruption/process ( e.g. ash clouds)
What is a secondary hazard?
Secondary hazards are the side affects or knock on impacts or primary hazards ( e.g. volcanic bombs)
Secondary hazards are sometimes more significant
What is a pyroclastic flow ?
A superheated mixture of ash, rock and dust. They travel down the sides of composite volcanoes at very high speeds with temperatures of over 400°.
What happened at the eruption of Mount Pinatubo?
Located on the Island of Luzon, Philippines in Asia. Here the Eurasian plate was subducted beneath the Philippine plate after more than 600 years of being dormant erupted on 12 June 1991.
It is a composite volcano so had andesitic lava causing an extremely explosive eruption. Caused steam clouds of 30km high and pyroclastic flows at speeds of over 200km/h.
What were the primary impacts of Mount Pinatubo eruption?
- Rescue was hampered due to ash clouds making the region darker
- Intense rainfall and landslides as typhoon Yunya occurred simultaneously
What were the secondary impacts of Mount Pinatubo?
- Winds were dispersed with gases like sulphur dioxide so average global temperatures dropped by 0.5°
- 847 people died due to primary impacts and many displaced
- 5000 Hines were destroyed and a further 7000 damaged
- hundreds more people dies due to diseases such as measles and pneumonia
- 800km2 if crops were destroyed
- heavy rain mixed with ash so caused intense lahars
What did Pinatubo response and management do?
- PHILVOLCS ( Philippines institute of volcanology and seismology) detected swarms of earthquakes beneath Pinatubo in Mach of 1991 suggesting magma was on the move
- Tiltmeters were installed to measure surface deformation
- Daily gas monitoring
- Geologists mapped routes of previous lahars to see where evacuation was potentially needed.
What did aid consist of?
- building dykes and dams to protect from lahars and flash flooding
- establishing farms away from danger zones
- converting an ex US air base into a means of shelter
- creating towns outside danger zones.
What is the focus and epicentre?
The focus is the point at which the original pressure is built up, the zone of subduction ( the Benioff zone) it is the point of rupture in the earths crust where energy is released. The epicentre is the point directly above the focus on the surface. The shock waves and vibrations are worst here.
What is a seismometer?
A way of measuring seismic activity and vibrations from the earth. Were the magnitude is worked out.
What are the primary impacts of earthquakes?
Ground shaking and rupturing
