Geologic Formations

Glacier Moraine

Piles of sediment in front of and along the sides of a glacier.

Disconformity

A missing layer caused by erosion, or a long span of time with no new deposits added.

Relative Age

Being able to tell which rocks are older or younger based on their position.

Inclusion

Bits of older rock that become part of a newer rock. Like when magma picks up bits of rock as it moves up through layers.

Original Horizontality

Sediments are added in horizontal layers.

Lateral Continuity

Sediments spread out in all directions until they thin out or hit a barrier.

Alluvial Fan

Triangle-shaped deposit formed when a river flows out onto the land.

Delta

Triangle-shaped deposit formed when a river meets a large body of water like a lake or ocean.

Angular Unconformity

Formed when rocks are folded, eroded, and then new sediments added on top.

Law of Superposition

In undisturbed layers, the oldest rocks are on the bottom, youngest ones on top.

Cross-cutting relationship

When a rock is cut by an event (like an earthquake), the rock has to be older than the event.

hanging valley

a valley that opens onto another valley, or as a cliff above a plain

mass movement

any type of erosion occurring as a result of gravity

rockfall

blocks of rock break loose from a steep slope, go airborne, crash into other rocks & knock them loose as well

cirque

bowl-shaped depression at the head of a glacier

weathering

breaking rock down into smaller particles

steep

describes a high angle of incline

transporting

glaciers erode sediment & deposit it somewhere else

glacier

large mass of ice and snow moving on land under its own weight

till

mixture of different sized sediments deposited by retreating glaciers

erosion

moving weathered sediment from one place to another

lahar

mudflow resulting from a volcano melting glacier ice

rock slide

occurs when LAYERS of rock suddenly slip downslope

creep

occurs when sediments (and trees!) shift slowly downhill

plucking

rocks are lifted by glacier water melting and refreezing around them

eskers

sediments left behind by a river of meltwater under the glacier

index fossil

species that existed briefly, but everywhere. Used in relative age dating.

mudflows

steep slope + heavy rain + little vegetation (sometimes called a mudslide)

deposition

the laying down of eroded sediments

slump

when a mass of material slips down along a curved surface