93262
Description
Flashcards by siobhan.quirk, updated more than 1 year ago
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Created by siobhan.quirk
over 11 years ago
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| Question | Answer |
| Igneous Rocks | those that have cooled from magma |
| Magma | molten rock |
| Lava | molten rock that cools at the surface |
| Silicic igneous rocks | have a composition rich in silica, of more than 66% and are light coloured (leucocratic) |
| Intermediate igneous rocks | Have a silica content of 66 to 52% and are grey (mesocratic) |
| Mafic igneous rocks | have a silic contnent of less than 45% |
| Felsic minerals | light coloured and silica rich |
| Mafic minerals | dark coloured, silica poor and rich in magnesium and iron |
| Cooling | igneous rocks may be at the surface or the depth |
| Extrusive | general term for all igneous rocks that cool at the surface - both lava and pyroclasts |
| Intrusive | term for igneous rocks that cool below the surface |
| Hypabyssal | igneous rocks form at relatively shallow depths below the surface |
| Plutonic | when igneous rocks form deep below the surface |
| Divergent plate margin | where two plates are moving apart and magma is rising up between them |
| Convergent plate margin | where two plates are colliding and magma is formed above a subduction zone or deep in the crust |
| Hot spot | formed by a fixed mantle plume bringing magma to the surface |
| Partial melting | occurs where some of the minerals in a rock melt to form a magma |
| Country rock | any rock, whether sedimentary, igneous or metamorphic into which an igneous rock is intruded |
| Minor intrusions | cool at hypabyssal depth below the surface and include sills and dykes |
| Major intrusions | plutonic and cool deep below the surface and include batholiths |
| Contact | where igneous rock meets country rock |
| Chilled margin | where the igneous rock has cooled rapidly so it has fine crystals |
| Baked margin | country rock that was heated and altered by the intrusion |
| Metamorphic aureole | large area around a batholith where the rocks have been metamorphosed |
| Pyroclast | an individual fragment ejected during an eruption |
| Pyroclastic | fragmental materials formed by explosive eruptions, including bombs, blocks, lapilli and ash |
| Volcano | a vent at the surface of the Earth through which magma and other volcanic materials are ejected |
| Pyroclastic rocks | are formed when the pyroclastic material is compacted into rocks |
| Pyroclastic flow | a hot mixture of pyroclastic material and gas. A nuee ardente is a type of pyroclastic flow |
| Isopachyte | a line joining points of equal thickness of a deposit such as ash. The maps may be called isopach maps |
| Lahars | mudflows of wet ash and volcanic debris that can flow rapidly down a mountainside |
| Viscosity | measure of a fluid's resistance to flow and controls the stickiness of a magma, which in turn depends on the silica content |
| Shield volcanoes | gentle slopes of less than 10 degrees and a roughly circular shape around a central vent |
| Fissure eruptions | where magma reaches the surface along long, linear cracks or fissures |
| Submarine eruptions | where magma comes from a vent or fissure on the sea floor |
| Low viscosity | where magma is fluid and flows freely |
| Effusive | term used to describe the fluid, non-explosive, basalt lava |
| Hawaiian eruption | large amounts of very fluid basaltic magma from which gases escape, but few pyroclasts |
| Strombolian eruption | more explosive with less fluid basalt and andesite lava. Regular explosions of gas and pyroclastic material |
| Vulcanian eruption | violent with viscous andesitic lava and large quantities of pyroclastic material from large explosions |
| Plinian eruptions | extremely explosive with viscous as-filled andesitic and rhyolite lava and tremendous volumes of pyroclastic material blasted out |
| active | volcano has eruptive activity within recorded history. Currently there are about 600 active volcanoes and each year 50 to 60 actually erupt |
| extinct | volcano has not shown any historic activity and is usually deeply eroded |
| dormant | volcano is one that has not shown eruptive activity within recorded history, but shows geological evidence of activity within the geologically recent past |
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