basic explanation to volcanoes formation
- high pressure inside earth keeps parts of mantle semi-molten
- when pressure is released, rocks become molten, hot molten rock is magma
- magma is less dense than rock around it, so rises up to earth’s surface
what is intrusive volcanic activity?
- takes place beneath the earth’s surface
- includes formation of large magma chambers and magma being forced into the crust through cracks in the rock
what is extrusive volcanic activity?
- takes place on the earth’s surface
- major form of this activity is volcanic eruptions of lava
- minor types of extrusive volcanic activity include hot springs, geysers, and boiling mud pools
what three things does intrusive volcanic activity form?
dykes, sills and batholiths
how does a batholith occur?
when large chambers of magma cools underground they form domes of igneous rock called batholiths
how do dykes occur?
where the magma has flowed into gaps in the surrounding rock and cooled it forms vertical dykes going across the layers of rock
how do sills occur?
where magma has flowed into gaps in the surrounding rock and cooled it forms horizontal sills going between the layers of rock
what are cooling cracks?
cracks that form when magma cools
they’re vertical in sills and horizontal in dykes
what are the 3 main types of lava? and what plate margins do they occur at?
- basaltic lava - constructive PM
- andesitic lava - destructive PM
- rhyolitic lava - destructive PM
what are the characteristics of basaltic lava?
- low silica content
- low viscosity (runny) - flows easily, gas can escape
- over 950oC
- eruptions aren’t violent, erupt frequently for long periods of time
what are the characteristics of andesitic lava?
- medium silica content
- medium viscosity, can forms blockages in vents
- 750-950oC
- pressure builds in blocked vents until released and creates violent volcano
what are the characteristics of rhyolitic lava?
- high silica content
- high viscosity (thick and sticky), flows less easily, forms blockages in vents
- less than 750oC
- pressure builds in blocked vents until released and creates violent volcano
what are the 4 type of volcano?
- dome
- caldera
- shield
- fissure
what are the characteristics of a dome volcano?
- layers of lava
- steep sides - caused by high viscosity lava flowing for short distances
- central vent
- rhyolitic or andesitic lava
where do dome volcanoes occur? example?
destructive plate margins e.g. Puy de Dome in France
what are the characteristics of a caldera?
- very wide circular crater, can be several km across
- central part of volcano has collapsed
- layers of lava or layers of lava, ash and cinders
- andesitic and rhyolitic lava
where do calderas occur? example?
destructive plate margins e.g. Aira Caldera in Japan
what are the characteristics of a shield volcano?
- layers of lava
- gently sloping sides - caused by low viscosity lava flowing for long distances
- central vent
- basaltic lava
where do shield volcanoes occur? example?
constructive margins e.g. Mauna Loa in Hawaii
what are the characteristics of a fissure volcano?
- layer of lava
- long, linear vent - few metres wide but several km long
- fairly flat surface caused by low viscosity lava flowing for long distances
- basaltic lava
where to fissure volcanoes occur? example?
constructive margins e.g. Laki Fissure System in Iceland
how does a hot spring occur?
if groundwater source of a spring flows close to an area of recent intrusive volcanic activity, the water is heated and so the spring becomes hot
what are the temperatures of a hot spring?
between 20oC and 90oC
example of hot spring
North Island, New Zealand
