How are igneous rocks formed?
- made when molten rock cools down and solidifies
- igneous rock type depends on how quickly the magma cooled and the composition of magma
- various minerals
- randomly interlocking crystals
- big air gaps, means it cooled down slowly (inside volcano)
- small air gaps, means it cooled down quickly (outside volcano)
How are metamorphic rocks formed?
- heat and pressure on sedimentary igneous rocks over long periods of time
- mineral and texture may be different to original rock, but chemical composition is the same
- as long as the rock doesn’t melt it is classified as metamorphic
- if it melts and turns to magma its gone
How are sedimentary rocks formed?
- layers of sediment laid down in lakes or seas
- buried in more layers over millions of year
- weight presses down and squeezes out the water
- fluids flowing through pores deposit natural mineral cement
Give an example of a metamorphic rock and what are the properties?
- marble
- a form of calcium carbonate
- very high temperatures and pressures break down the limestone and reforms as small crystals
- giving marble a more even texture and making it harder
Give an example of a igneous rock and what are the properties?
- granite
- very hard
- ideal for steps and buildings
Give an example of a sedimentary rock and what are the properties?
-limestone
-mostly formed from seashells
original shells mostly crushed, but fossils can remain
How are volcanoes formed?
- oceanic plates are denser than ontinental plates
- oceanic plates are also cooler at the edges –edges sink easily, pulling the oceanic plate down
- as the oceanic crust is forced down underneath continental crust (subduction) it melts and starts to rise
- if this molten rock finds a way to the surface volcanoes form
How do geologists try to predict volcanic eruptions?
- looking at signs that a volcano eruption might happen
- e.g.magma movement below the ground near a volcano
Why do geologists try to predict volcanic eruptions?
- to try and find out if there are signs a volcano may erupt soon
- spotting these things means scientists can predict eruptions with greater accuracy than in the past
- tricky as volcanoes are unpredictable
- scientists can most likely just say when an eruption is more likely to happen than usual
Why do people choose to live near volcanoes?
-volcanic ash creates fertile soil
How do volcano eruptions differ?
- volcanoes that form iron-rich basalt, eruptions have runny lava and eruptions are safer
- silica-rich rhyolite magma, eruptions are explosives, producing thick lava that can be blown violently from the top
What is subduction?
- two tectonic plates colliding
- dense oceanic plate is forced underneath a less dense continental plate
