1. 10.3 intrusive igneous activity

2. Some review…
Volcanic rock that cools and hardens covers much of Earth’s surface.
Most magma, however, cools and hardens deep within the Earth.
This magma forms the roots of mountain ranges and a variety of landscape features.

3. Some review…
Recall that magma rises through the crust toward the surface.
As it rises, it may rise through fractures in the rock or force it’s way between layers of rock.
The magma may form thin sheets a few centimeters thick or collect in vast pools that can be kilometers wide.
All these formations have various names; dikes, sills, laccoliths and batholiths.

4. Classifying plutons
The structures that result from the cooling and hardening of magma beneath Earth’s surface are called plutons.
Plutons form in continental crust wherever magma slowly crystallizes and forms intrusive igneous rock.
Recall that intrusive igneous rock is rock that forms as magma cools deep within the Earth. Extrusive igneous rock forms once magma emerges as lava and cools above earth’s surface.

5. Classifying plutons
Over millions of years, uplift(rising) and erosion can expose plutons to the world above the surface.
There are several types of plutons:
Sills
Laccoliths
Dikes
batholiths

7. Sills and Laccoliths
Sills and laccoliths are plutons that form when magma intrudes between rock layers near the surface.
Sills and laccoliths differ in shape and often differ in composition.
A sill is a pluton that forms when magma flows between parallel layers of sedimentary rock.
Usually horizontal

8. Exposed sill

9. Sills and Laccoliths
A laccolith is a lens-shaped pluton that has pushed the overlying rock layers upward.
Like sills, laccoliths form when magma intrudes between sedimentary rock layers close to the surface.
The magma that forms laccoliths has a higher viscosity (thickness) than the magma that forms sills.
For this reason, the magma that collects bulges upward instead of spreading out in a thin layer.

10. Dikes
A dike is a pluton that forms when magma moves into fractures that cut across rock layers.
Usually Vertical
Dikes are sheet-like structures that can range in thickness from less than a centimeter to more than a kilometer.
Most dikes are a few meters thick and extend for no more than a few kilometers.

11. Dikes
Exposed dike

12. Batholiths Batholiths are very large bodies of intrusive igneous rock.
A batholith is a body of intrusive igneous rock that has a surface exposure of more than 100 square kilometers.
Much larger than a laccolith, a batholith can be hundreds of kilometers long and tens of kilometers across.

13. Batholiths
Batholiths form from many individual plutons that begin as blobs of magma deep beneath the surface.
The plutons slowly rise through the crust in the form of hot magma.
They clump together forming a huge irregular mass of underground magma, molten rock.

14. HW assignment
Use the internet to research and write 3 paragraphs about one of the following geological formations. Describe how it was formed. DO NOT COPY CUT OR PASTE: each paragraph must be a minimum of 4 sentences.
The Giants Causeway in Northern Ireland
The Northern Canadian Rocky Mountains
Devil’s Tower, Wyoming
Mount Shasta, California
Crater Lake, Oregon