By Gravity, Wind, and Water Weathering & Erosion By Gravity, Wind, and Water

What is “weathering?” Weathering is the break down of rocks that have been exposed to the atmosphere Chemical Weathering rocks break down as their minerals change in composition (they become different substances) Physical Weathering rocks are broken down into smaller pieces without changing their composition

Factors which affect the rate of weathering: 1.)The amount of material exposed * greater surface area= more weathering 2.) Particle Size- smaller particles= more surface area 3.)Climate- *Chemical weathering: hot & wet *Physical weathering: cold or warm and dry, alternating cold and cool & wet (Frost Action) 4.) Mineral Composition: -Chemical: some minerals react with acid -Physical: Some minerals are more durable/ have a greater hardness

small particles (high surface area)=fast weathering *small particles (high surface area)=fast weathering *Large particles (low surf. area)= slow weathering

Physical or Chemical Weathering dominant in an area depends upon its climate

Types of Physical Weathering: 1.)Ice wedging/frost action water enters small cracks in the rock Water freezes expands forces the cracks to open more repeats until the rock breaks apart

2.) Wetting and drying breaks up rocks made from clay When wet they expand, and as they dry they shrink As this repeats over and over, the clay becomes weak and cracks

3.) Exfoliation or “Unloading” -when rocks are uplifted and exposed the pressure on them ↓ -rock surface then expands and “sheds” its layers

4.) Plant Growth Root wedging from trees Lichens and Moss break apart surface of rock

5.) Abrasion by Water: tumbling  Spheroidal pebbles Water carries sediments and tumbles them eventually making them smooth

6.) Abrasion by Wind Arid regions with little or no vegetation carry airborne sediments in wind currents which over time smash and erode the rock surface

Chemical Weathering 1.) Oxidation oxygen reacts with some minerals, especially those containing iron (magnetite) to form rust (called iron oxide)

2.)Carbonic Acid aka “Acid Rain” Water in atm. mixes with CO2 to form weak acids

Rocks/ Minerals that weather with acid: 1.) Calcite (mineral) 2.) Limestone (made of calcite) 3.) Marble (made of calcite)

Weathering from Carbonic Acid also creates caves and sinkholes Weathering from Carbonic Acid also creates caves and sinkholes. These areas are referred to as “Karst” topography

Looking at karst topography from the surface (you can see the rock dissolved along the joints)

Calcium Deposits (Stalactites and Stalagmites!)

When enough of the limestone is dissolved under the ground, it will collapse forming a sinkhole! Man killed in Sink Hole News Clip

Anywhere that’s underlain by large volumes of limestone is a risky area to build on

3.) Natural Acids: Organic Acid from decaying plants in soil Sulfuric Acid from volcanic activity/hot springs

4.) Hydrolosis water (hydro) reacts with minerals such as feldsparforms clay

ROCKS VARY IN RESISTANCE TO WEATHERING

The more resistant rock will be eroded less than the weaker ones

And the weaker ones more…

Devils Tower, Wyoming All that remains of this ancient volcano is the central “plug” of solidified and very weather-resistant igneous rock

EROSION PART II Erosion is the TRANSPORT of weathered materials!

Part II: AGENTS OF EROSION These are the forces or materials that transport or move sediments: Gravity Wind Running water (streams/ rivers) Glaciers Waves

Erosion by Gravity (the most powerful one!) When gravitational force is greater than the force friction of the land, movement occurs! These are called Mass Movements -Soil creep -Avalanches -landslides -Pyroclastic -Mudflows -Rock falls

Evidence of Soil Creep

Mass Movements Video Links Click Below: Rock Slide in TN Mudslide in Afghanistan Avalanche in Alps

2.) Wind Erosion aka Abrasion/Deflation *Dependent on: Wind Velocity* * . As sediment size _________, the amount of erosion by wind _________. (because lighter to carry)

3.) Water *The faster water flows, the heavier and larger objects it can erode and transport

The greater the velocity, the larger the particle diameter it can carry! Q: at what velocity can pebble size particles be transported? If it is under this, it will be deposited!

Because of variations in velocity, there is deposition & erosion in different areas along a river This means river profiles differ according to the velocity *A stream is deepest where the current is the fastest

4.) Erosion and Deposition by Ocean Currents and Waves Surface ocean currents and waves are generated mostly by wind. Wave action Energy within a wave is propagated through a transverse wave Circular motion within a wave results in the movement of sediments

Circular motion in a wave Wave action animation

As waves crash into the shoreline, they erode the bedrock animation

Erosion of sand from areas causes deposition in others: Longshore Currents Beach Deposition of sediments by ocean waves Sand Bars Sediments deposited by long shore currents Barrier Islands Large sandbars

NY Barrier Islands: South Short of Long Island!

Long Beach Long Island NY