volcanoes

• Pyroclastic flows are fast-moving currents of hot gas and volcanic matter that flow down the sides of a volcano during an eruption.
• intrusive rocks cool slowly over hundred of millions of years below the earths surface where its more insulated
• extrusive rocks cool faster and produce finer grained rocks
• ultramafic/mafic rocks have higher magnesium and iron concentrations and are darker in colour, form at higher temperatures
• felsic rocks have higher silicate concentrations and form at lower temperatures. often pink/white in colour
• melting point of rocks depends on pressure, volatiles (water), temperature, and rock type
• earths initial heat came from asteroid impacts, compaction, core formation
• earths current heat source comes from decay of radioactive elements in the mantle and core like potassium and uranium
• mantle plume is an area of rising mantle which heats surrounding rock. creates a hotspot in the earths crust.
• decompression melting is where hot magma rises to an area of low pressure and heats surrounding rock to form new magma. creates younger crust, eg mid ocean ridge.
• adding water helps lower melting point of rocks as it helps break the crystal structure of the rock. often happens at subduction zones
• a sill is a flow of magma that follows bedding planes underground. follows lines of weakness, seen at the dasses in holyrood
• a dyke is where a magma flow cuts across bedding planes and sedimentary units. can be seen across the Salisbury crags in holyrood
• a stock is an area where magma cools before it reaches the surface of a volcano, like a mini magma chamber, magma reaches surface through a volcanic neck
• a batholith is a solid magma chamber that has cooled very slowly as it is near the earths surface but hasn't erupted.
• a laccolith is a chamber of cooled magma coming from a dyke. it creates a dome shape as more magma is deposited in it and cools.
• hypabyssal rocks are medium grained rocks that aren't extrusive but also didnt cool as slowly as deep intrusive rocks
• plutonic is another word for deep intrusive rock
• oceanic crust is comprised of - deep plutonic zones, mainly gabbro, course grained; sheeted dykes, hypabyssal zone, connects magma to surface; pillow basalt, basaltic lava flows, erupted lava into lava, cools quickly, glassy crst, interior inflates and forms pillow texture; sediment layer
• a porphyritic rock texture is when there are two crystal sizes,l larger ones surrounded by smaller ones called the matrix, shows two phases of cooling
• a vesicular rock texture is where the magma contained gas bubbles which expanded as it was erupting, the magma solidified before the gas bubbles could pop forming a vesicle. stretching gas bubbles can show direction of magma flow, amygdaloidal texture is where vesicles are filled in by a new mineral, typically from dissolved minerals in precipitation.
• volcanic explosivity index is a range of values which measure how explosive a volcano is 0 being non explosive and 8 being most explosive in history, each VEI is 10x more explosive than the last.
• volcanic ash can cause sunlight to be blocked out causing global cooling and crop failure. eg 1816, mt tambora caused a volcanic winter
• volcanic eruptions can cause tsunamis due to water being displaced by pyroclastic material falling into water.
• many people live by volcanoes due to their geothermal energy source. magma heats water and produces steam, this steam turns turbines to generate electricity. can drive tourism, blue lagoon hot springs in iceland. also created fertile soil due to addition of minerals like potassium, iron and phosphorus.
• effusive style eruptons are when lava ooze out of the vent. magma has low viscosity and low gas and water content. hot lavas magnesium and iron rich
• explosive style eruptions produce tephra as lava has high viscosity and magma fragments into pyroclastic fragments, high gas and water content which expands rapidly creating the explosive eruption
• hydrothermal eruptive material is comprised of mainly of hot water and no magma, explosive pulversied rock produces ash, eruptions are generally small and short
• phreatic eruptive material is where water interacts with old magma which heats it creating explosive eruptions producing ash.
• phreatomagmatic eruptive material is where new magma and water interact creating a very explosive eruption
• flood basalt eruptions are large scale effusive eruptions, they have a short duration but high lava volumes that are hot and runny with a basaltic composition that create lava plateaus and mountain ranges
• blood basalt eruptions form by large mantle plumes hitting the base of the crust causing melting. a plume can tear a continent apart, these eruptions split pangea
• some volcanoes exist in the solar system. planets like mars and venus show signs of volcanoes, on mars they arent active but venus is volcanically active.
• we can sometimes predict if volcanoes are going to erupt by looking at hot springs. water comes into contact with hot rocks which creates a hot spring at the surface. can generate a mineral rich bath, formation of new springs or activation of old ones indicate magma is moving.
• geysers are underground cavities of water that us heated by magma and rock, water vaporises generating a pocket of steam which rapidly rises and displaces water above it which shoots into the air. this can be a sign of a potential eruption is changes are seen in geyser behaviour
• since volcanos