Erosion & Deposition - PowerPoint Presentation

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Erosion & Deposition

The creation of sedimentary rocks

Weathering and Mass Movement

Objectives:

1. Describe the processes by which erosion wears down and carries away rock

2. Distinguish between chemical and mechanical weathering3. Describe the factors that affect the rate of weathering4. Explain how the force of gravity contributes to erosion by mass movement

Erosion

Definition: erosion is the process that wears

down

and carries away rock and soilErosion is associated with movement from one place to anotherErosion acts through weathering, the force of gravity, and through movement of streams, groundwater, glaciers, wind and wavesErosion breaks down the tallest mountains over time

Weathering

Definition: weathering is the process by which rocks are chemically altered or physically broken down into fragments at or near Earth’s surface

There are 2 types of weathering: mechanical and chemical

Both processes cause rocks to disintegrate and decomposeDefinition: mechanical weathering is the process of physically breaking rock into smaller fragments

Definition: frost wedging is physical weathering due to water seeping into cracks and expanding due to freezing

Many road potholes are the result of frost wedging

Definition: abrasion is physical weathering caused by the process that occurs when rocks scrape or grind against each other

This can occur by water or wind

Plant roots cause physical weathering by growing into cracks breaking rocks apart

Erosion causes physical weathering by removing material from the surface of the rock, releasing pressure on the rock causing the outside to crack and flake

Definition: chemical weathering in a process in which rock is broken down by chemical reactions

Water is the main reactant in chemical weathering

Chemical reactions dissolve the minerals that make up the rocks or changes them into new materials

Water and carbon dioxide combine to form carbonic acid producing acid rain

Acid rainwater dissolves many mineralsRusting, which is a kind of oxidation, occurs in minerals that are rich in iron

Factors that Affect the Rate of Weathering

There are 3 main factors that determine how fast mechanical and physical weathering take place

They are temperature, availability of water and the type of rock

Certain rocks like limestone and marble undergo rapid chemical weathering since their main mineral (calcite) dissolves in waterSlate, quartz and mica are more resistant to chemical change

Mass Movement

Definition: mass movement is the downward movement of rock and soil due to gravity

Definition: the rapid movement of large amounts of rock and soil is a landslide

Landslides often happen after heavy rainDefinition: mudflow is rapid mass movement of soil & other sediment with waterAfter rain water loosens the sediment, increases its weight and causes it to flow

Definition: creep is the gradual slowing down of soil that is moving down a slope

Creep usually occurs due to ice

Creep happens so slowly is often hard to notice

Definition: slumping occurs when weak layers of soil or rock move downslope as a single unitGravity acting on water saturated soil and rock causes slumping

Water Shapes the Land

Objectives:

1. Explain how running water erodes the land

2. Identify features formed by erosion and deposition due to running water3. Describe how caves and sinkholes are formed by groundwater erosion

Running Water & Erosion

Definition: deposition is the process in which sediment is laid down in new locations

Deposition is a type of erosion

Most sediment is moved by running waterRunning water erodes the landDefinition: saltation is the process of particles bouncing along a stream bottom

A large amount of deposition with a fast moving water source increases erosion

Speed increases a streams ability to erode

Features Formed by Erosion

Water erosion form v-shaped valleys, waterfalls, meanders and oxbow lakes

Near its source the stream moves fast, causes valley’s sides to become steeper & sharply angled creating a V

V-shaped valleys can contain rapids and waterfallsWaterfalls develop where a stream crosses rock layers that differ in hardnessThe harder layers resist erosion for the top of the waterfall while the other layers are worn away creating the cliff over which water tumbles

Definition: a flood plain is the flat area along a stream that is entirely covered only during times of flood

During flooding, erosion may further widen the valley

Definition: a meander is a looplike bend in the river caused by sediment being deposited on the outside of a curve in the river

Features deposited by flowing water include alluvial fans and delta

Definition: an alluvial fan is sediment that has settled out as the stream flows out of the mountains creating a fan-shaped deposit

Definition: a delta is mass of sediment that was carried & deposited by a stream that flows into a lake or ocean where the water slows down

The delta is located where a river enters a large body of water

Groundwater Erosion

The processes of chemical weathering causes groundwater erosion including the formation of caves and sinkholes

Acid rain moves through the ground reacting with some rocks

Limestone easily erodes away forming caves and cavernsSometimes water drips into the cavern from rock layers above

Definition: a stalactite is an icicle-like formation of minerals created from water dripping from the ceiling of the cave

Definition: a stalagmite is a pillar of minerals created from water dripping down to the floor

Definition: a sinkhole is an entire portion of ground that has collapsed due to erosion weakening a layer of limestone

Areas of southern and central US have many sinkholes

EXAMPES OF SEDIMENTARY ROCK