Topic 1 - Earth Structure + Volcanos/tsunamis (set B)✔️ Flashcards
What is the lithosphere/crust ?
Crust is the surface of the earth and is split into tectonic plates made up of silicon based rocks
What is the astenosphere?
Upper layer of the mantle - semi molten
what is the mantle?
Largest part of the earths layers - made of silicon based rocks - part nearest to the core is quite rigid - temp of mantle between 1000 and 3700 degrees
What is the inner core?
Very dense centre with temps of 4400 to 6000 degrees - made of iron and nickel
What is the outer core?
Less dense then the inner core and is made of liquid iron and nickel - temp 4500 to 5500 degrees
What are the two types of earths crusts? what are there features?
-continental crust - 30 to 50km thick and less dense mostly made of granite
-oceanic crust - 6 to 8 km thick and light but dense and made of basalt
Why do tectonic plates move?
Tectonic plates always moving due to convection currents in the mantle
Explain the process of convection currents in the mantle?
Radioactive decay of elements in the mantle generates lots of heat - lower parts of the mantle heat up and become less dense and slowly rise - they cool down and become more dense and slowly sink - drags on base of tectonic plate and causes movement
What fuels convection currents?
Radioactive decay of elements like uranium and thorium in the mantle and core
What happens at convergent boundaries?
1)Oceanic plate meets a continetal plate and oceanic is submerged into the mantle and destroyed often creating volcanos and ocean trenches
2)continenetal plate meets continental no subduction - they collide forming fold mountains
What are plate boundaries?
Where tectonic plates meet creating three types of boundarys
Products of convergent boundaries?
- fold mountains
- composite volcanos
- ocean trenches
What happens at divergent boundaries?
Two plate move away from each other - eg at mid Atlantic ridge - magma rises from the mantle to fill gap and cools creating new crust
Product of divergent boundaries?
New crust formed
Underwater shield volcanos formed
What happens at conservative boundaries?
Two plates moving sideways past each other in the same direction - they become stuck and pressure builds up until plate can break free causing earthquakes - crust is not created or destroyed
Products of conservative boundaries?
Earthquakes
Where do composite volcanos occur?
Occur at convergent plate boundaries - subducted oceanic contains lots of water which reacts with magma and creates gasses which causes subducted crust to erupt
Features of composite volcano?
- explosive eruptions and deposit a layer of ash
-erupt andesitic lava which has a high silica content which makes it thick and sticky cant flow
Features of shield volcanoes?
- occur at hotspots or divergent plate boundaries
- not very explosive made up of only lava
- erupt basaltic lava which has low silica content and is runny - flows quickly and spreads
What is the structure and features of andesitic lava?
- high silica content makes it thick and sticky and can not flow far
What is the structure and features of basaltic lava?
Has a low silica content and is runny - flows quickly and spreads over a wide area
Where do shield volcanos form?
Occur at hotspots or divergent plate boundaries
How do hotspot volcanos form?
Occur where a plume of hot magma from the mantle moves towards the surface which can break through the crust and reach the surface causing an eruption and a shield volcano forming - hotspots remain stationary but crust moves above them which creates a chain of volcanic islands
How was Hawaii formed?
Is a chain of volcanic islands in the middle of pacific plate cause by hotspots and the crust moving above them
What is a tsunami?
Series of ocean waves usually created by volcanic or earthquake activity under the ocean can reach over 30 m high
how do tsunamis form? What happens just before they hit?
When an earthquake or volcano happens on the ocean floor it displaces water - which once it reaches shallower water begins to slow down and grow in height - hard to detect but coastal water starts to retreat just before wave hits coast
