Ch. 18 Notes Day 3

Objectives SWBAT explain the difference between intrusive and extrusive volcanic features SWBAT describe the different types of volcanic intrusions, and how they are classified by size and how they intrude existing rock

Intrusive vs. Extrusive Volcanic Activity Magma does not reach the earth’s surface Magma cools within the earth’s crust to form igneous rock formations These formations can be eventually exposed to do erosion, earthquakes, or other activity Magma reaches the earth’s surface and becomes lava Extrusive activity also includes geysers, and gas eruptions The lava eventually cools on the earth’s surface Cinder cones, composite volcanoes, shield volcanoes, and calderas are all examples of extrusive volcanic formations.

Intrusive Activity

Molten Magma is less dense than surrounding rocks. This forces magma to move upward intrude into, the overlying crust.

Intrusive Activity can effect the crust in three ways: A. Magma can break the overlying rock apart and enter the newly formed fissures. B. Magma can also cause blocks of rock to break off and sink into the magma, where the rocks may eventually melt. C. Magma can also push and move surrounding rocks causing “lumps” and “bumps”

Plutons Plutons are intrusive igneous rock bodies that can be exposed at Earth’s surface as a result of uplift and erosion and are classified based on their size, shape, and relationship to surrounding rocks.

Plutons

Batholiths Batholiths, the largest plutons, are irregularly shaped masses of coarse-grained igneous rocks covering at least 100 km2 and take millions of years to form.

The Sierra Nevada and San Gabriel mountains are large Batholiths

Stocks Stocks are irregularly shaped plutons that are similar to batholiths but smaller in size.

Laccoliths A laccolith is a mushroom-shaped pluton with a round top and flat bottom resulting from a Magma intrusion into parallel rock layers close to Earth’s surface.

Laccoliths

Sills A sill is a pluton, ranging from only a few centimeters to hundreds of meters in thickness, that forms when magma intrudes parallel to layers of rock.

Sills

Dikes A dike is a pluton, ranging from a few centimeters to several meters wide and up to tens of kilometers long, that cuts across preexisting rocks.

Dikes

Dike Near Shiprock, NM

Dike Near Shiprock, NM

Dike Near Shiprock, NM