Assignment Check Igneous Rock
Hot Spots
- unusual because they are not related to the plate boundaries -derived form deep localized heat source -*Intraplate* volcano activity
Convergent boundaries ex.
-Aleutian islands andes/ mt. st. helens
where do most volcanoes occur
along the dyes of plates
tephra
ash, rock, fragments, bombs
characteristcics of igneous rock
color;light/dark texture/Crystal size: large/coarse or small/fine cooling rate: fast or slow
laccolith
domelike structure formed when magma pushes rock layers above it upwards
Divergent boundaries
ex. Mid- Atlantic ridge and Iceland -lava flows form the rift- which makes new land in the middle
how do volcanoes form?
magma is less dense than rock around, so it is forced up towards the surface
intrusive rock
molten magma that cools slowly beneath surface -slow= large crystals -granite; contains mica, feldspar
Cinder cone
steep and conical -explosive eruptions throw lava and rock high in air (tephra) -built from ejected lava fragments
Crater
steep walled depression around the vent
dike
vertical structures formed when magma cuts across layers and hardens into igneous rock
vent
where lava flows out
2 important factors control whether an eruption will be explosive or quiet
-amount of silica -amount of water vapor and other dissolved gases
explosive volcano (3)
-high silica -high viscosity -high gas content
extrusive rock
-molte material cools on Earth's surface -fast cool= small crystals (no visible crystals) -ex: obsidian, pumice, basalt
Magma
-molten material beneath Earth's surface
how is igneous rock formed?
-molten material magma from a volcano deep inside the earth cools and crystalizes into rock
Composite volcanoes
-mostly found where one plate sub ducts under another -alternating layers of lava and tephra -VERY EXPLOSIVE - Mt ST. Helens in Cascade Range
shield volcanoes
-quiet eruptions of basaltic lava spread out in flat layers -broad volcano with gentle slopes -hawaii (mt Kailua& Maunaloa)
Convergent boundaries
-the more dense Op sub ducts under the less dense CP and is driven down into the mantle -sub ducted plate melts due to the heat and friction causing the magma to rise up and create volcanoes
Hot Spots ex.
Hawaii islands sit on top of a hot spot
Caldera
large depression that occurs when the top of the volcano collapses
batholith
large, irregularly-shaped structures of hardened magma that extends deep into the Earth's crust
lava
outside of Earth's crust
Viscosity
resistance of a liquid to flow- its thickness
sill
sheetlike structure formed when magma between rock layers hardens into igneous rock (horizontal)
