What kind of igneous rock would you expect to find at the base of a volcano and why?
99355
igneous extrusive basalt
1016696
Volcanoes are the result of the dynamic of Earth.\nEarth's crust is broken in many blocks (tectonic plates) that are in motion respect one another. Mostly of volcanoes are located along boundaries of adjacent plates.\nVolcanic eruptions near tectonic plates' boundaries are driven by the magma that ascend from deeply beneath the crust\n\nScientific predict volcanic eruptions by studying some geophysical and geochemical parameters:\n * increasing of the seismic activity near the volcano\n * changes in the quantity of gases (CO2, SO2, etc) expelled by the volcano\n * observed changes in magnetic or geoelectrical explorations: studying the surface of the volcano with magnetic geoelectrical methods.\n\nYou can read more at links below
147972
Water.\n\nWater is one of the key parts of the formation of magma in subduction zones. The water that is in the subducting plate lowers the melting point of the rock by a few hundred degrees C. The water in the subduction plate will boil and migrate upwards into the overlying wedge of mantle rock where it will reduce the melting point of the overlying mantle. This magma will migrate upwards and form a volcano. \n\nAnother part of this process is that within rock there are many different minerals, all with different melting points, so the ones that melt at the lowest temperatures tend to form magma first, so the resulting magma comes from a partial melt of the source rock.\n\nHere's another diagram (I'd draw you my own but I can't post anything but text here):\nhttp://earth.leeds.ac.uk/dynamicearth/subduction/cordillera_islandarc.htm
740828
There are two\nINTRUSIVE\nthe magma cooled of slowly, leaving gross crystals (granit)\nEXTRUSIVE\nthe magma cooled off fast, leaving crystal so small you can't see them (basalt)
905674
There are mainly 2 broad classes of magma, rhyolitic and basaltic. Due to the chemical characters(more mg and fe) of the basaltic magma, it is denser but less viscous than the acidic (rhyolic) magma.  The rhyoltic lava due to its excess silica content are highly viscous and due to this reason after eruption from the plate collision site(normally we find volcanic eruption where an ocenic plate subducts beneath a continental plate though there are another kind of volcanic site called hotspot volcano which can be anywhere regardless of the plate position)it mounts up significantly but the basaltic lave flows downslope and  cannot mount up ( eg Deccan Trap in India and the whole ocean crust).  So we find the volcanoes are mainly made up of rhyolitic lava.
660018
Different kinds of volcanos.. Shield, cone etc.\nJust the way the lavva flows out and the ash spits up./
55066
Volcanoes are one of the main ways that igneous rocks are deposited on the surface of the earth. Other igneous rocks form by cooling of magma within the earth and do not reach the surface. These are called intrusive igneous rocks. \n\nOne of the models to explain how our atmosphere was created suggests that volcanic activity released both water vapor and other gases. The present day atmosphere has changed its composition from the original because of the plants that have released oxygen from carbon dioxide.  Current estimates are that volcanic gases contribute 110 million tons of carbon dioxide per year while man's contribution is about 10 billion tons a year. \n\nVolcanoes also contribute other gases and airborne particulates to the atmosphere that can have adverse affects on the environment for several years after a major eruption. Sulphur dioxide is present in most volcanic eruptions and this changes to acid rain as it is dissolved in the atmosphere. This is very harmful to plant life and damages healthy soil. Volcanic ash is often ejected high into the atmosphere and remains there for many years before settling back to earth. This has been speculated to have been the cause of global periods of colder weather  that occured in the 400's and in prior times. \n\nThe formation of intrusive igneous rocks also involves this outgassing of carbon dioxide and other gases, but because it takes place very slowly and often deep underground it has a very gradual effect on the atmosphere. Much of the gas that comes from these rocks will stay traped by being dissolved in water that remains in the subsurface. The movement of this water actually is responsible for many mineral deposits of things like copper ore.
93724
...a composite volcano.\nThese types of volcanoes are built up of layers of lava, ashfall, tephra, cinder, etc.   One name is stratovolcano (strato- refers to the layers, and the other is composite, which refers to the fact that the volcano is made up of many types of material.\nFor more information on stratovolcanoes:\nhttp://vulcan.wr.usgs.gov/Glossary/StratoVolcano/description_composite_volcano.html
871525
A stratovolcano is a tall, conical volcano composed of many layers of hardened lava, tephra, and volcanic ash. These volcanoes are characterized by a steep profile and periodic, explosive eruptions. The lava that flows from them is highly viscous, and cools and hardens before spreading very far. The source magma of this rock is classified as acidic, or high in silica to intermediate (rhyolite, dacite, or andesite. or basalt). This is in contrast to less viscous basic magma that forms shield volcanoes (such as Mauna Loa in Hawaii), which have a wide base and more gently sloping profile. Many stratovolcanoes exceed a height of 2500 m.\n\nStratovolcanoes are a by-product of the subduction of tectonic plates. The source melts of these volcanoes arise as a result of the dewatering of oceanic crust at specific pressure/temperature conditions as the plate subducts to lower depths. The water freed from the subducting slab allows partial melting of the overlying mantle rock, which rises due to its lower density relative to the surrounding mantle rock, and pools at the base of the crust. The melt is initially basic in composition. As it rises through the crust, it incorporates more acidic adjacent crustal rock, leading to a final intermediate composition. The water remains in the melt and upon eruption contributes to the explosive power of these volcanoes as superheated steam.\n\nAlthough stratovolcanoes are sometimes called composite volcanoes, volcanologists prefer to use the term stratovolcano to distinguish among volcanoes because all volcanoes of any size have a composite (layered) structure — that is, are built up from sequential outpourings of eruptive materials.
1177665
Hmmmmm ..... some volcano probably??   You probably know that - can't think of one that fits.
171052
according to my source it is a volcanic remnant being... um, harvested (for lack of a better word) for lava rock.  Just a note, most active or recently (in geological history, not ours) active volcanos can be told by thier names, generally being called Mount ______, instead of ________ Mountain.  try it :)
225608
Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be derived from either the Earth's mantle or pre-existing rocks made molten by extreme temperature and pressure changes. Over 700 types of igneous rocks have been described, most of them formed beneath the surface of the Earth's crust. The word "igneous" is derived from the Latin ignis, meaning "fire".\n\nIgneous rock are classified according to mode of occurrence, texture, chemical composition, and the geometry of the igneous body.\n\nIgneous rocks make up 95% of the Earth's upper crust.
34766
Most igneous rock is formed deep in the earth where it is very hot.  Igneous means fire, similar to ignition which fires a spark plug in an engine.  Igneous rock may be formed at or near the surface of the earth when volcanoes erupt and lava flows.  The rock closest to the lava heats up most and becomes more igneous than rock further and further away.  There is usually a clear change in coloration of the affected rock because its crystal minerals are altered by the heat.  Lava can flow following existing cracks in rocks and partially transform the adjacent rock to igneous foorms as it cools.
823697
The primary one is a lava tube, a pathway that magma filled and left after cooling, long tunnels that are a way of magma flowing out of the central vent area.\n\nFar underground, you can find the magma chamber, or a solidified magma chamber- a pluton.
963629
granite....sand...\nhttp://images.google.com/imgres?imgurl=http://library.thinkquest.org/05aug/00461/images/igneous.jpg&imgrefurl=http://library.thinkquest.org/05aug/00461/igneous.htm&h=423&w=640&sz=262&hl=en&start=17&tbnid=1_Wjmt6u5ghPyM:&tbnh=91&tbnw=137&prev=/images%3Fq%3Digneous%2Brocks%26svnum%3D10%26hl%3Den%26lr%3D\n\n\nthe most common....basalt...\nhttp://images.google.com/imgres?imgurl=http://www.learner.org/channel/courses/essential/earthspace/images/show5-brit-with-igneous.jpg&imgrefurl=http://www.learner.org/channel/courses/essential/earthspace/session3/closer.html&h=300&w=300&sz=28&hl=en&start=14&tbnid=iEnzTA6MoGvW4M:&tbnh=116&tbnw=116&prev=/images%3Fq%3Digneous%2Brocks%26svnum%3D10%26hl%3Den%26lr%3D\n\n\npumice...\nhttp://images.google.com/imgres?imgurl=http://www.otago.ac.nz/geology/features/rocks-minerals/pumice.jpg&imgrefurl=http://www.otago.ac.nz/geology/features/rocks-minerals/rocks.html&h=667&w=800&sz=47&hl=en&start=6&tbnid=QxNtL7z7RM7VCM:&tbnh=119&tbnw=143&prev=/images%3Fq%3Dpumice%26svnum%3D10%26hl%3Den%26lr%3D\n\nobsidian...\nhttp://images.google.com/imgres?imgurl=http://faculty.icc.edu/easc111lab/labs/labb/rocks/ibox.jpg&imgrefurl=http://faculty.icc.edu/easc111lab/labs/labb/igneous.html&h=330&w=265&sz=59&hl=en&start=47&tbnid=6qFg9tv5UzEBnM:&tbnh=119&tbnw=96&prev=/images%3Fq%3Digneous%2Brocks%26start%3D40%26ndsp%3D20%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DN
36455
The common name of such a type of rock is obsidian.
232163
Yahoo search on images of volcanos:\nhttp://img.search.yahoo.com/search/images?fr=slv2-&ei=UTF-8&p=volcano