volcanoes 12 3 notes 08 09

Igneous Rock Features

• Igneous- “from fire”, one of 3 major types of rock • Most magma cools & solidifies underground to form

hard, very dense rock

– Result in different sizes and shapes of rock bodies that are visible at the surface when the overlying rock is weathered and eroded away

– Called intrusive when they form below the surface

– Slow cooling causes rock to have large crystals

Most common are:

• Batholiths

• Dikes

• Sills

• Volcanic necks

also

• Calderas

Batholiths

Batholiths

Baja Batholith (southern CA)

Batholiths

The largest intrusive rock bodiesCan be many hundreds of kilometers wide

and long, and several kilometers thick

Yosemite National Park in CA

Yosemite National Park in CA

What is the difference between a dike and a sill?

Dikes

Ship Rock, NM

Morocco

Sills

Sills

Sills

Volcanic necks

Devil’s Tower, WY

Volcanic necks

• Magma inside vent hardens

• Softer rock of cone and surface weathers and erodes away

• Hard, dense igneous rock is exposed

Calderas

an unusually large crater or the remains when the cone collapses into its own magma chamber

Formation of Crater Lake