Weathering, Erosion & Deposition

THINK!!!! Imagine the tiniest rock you have ever found. How did it get so small? It didn’t start out that way! What forces created this rock?

Weathering is the breaking down of rocks and other materials on the earth’s surface

What is the difference between weathering and erosion?

Weathering - processes at or near Earth’s surface that cause rocks and minerals to break down by air, water, plants and animals Erosion - process of removing Earth materials from their original sites through weathering and transport by water, wind or gravity

What are the two types of weathering?

Mechanical/Physical Weathering 2 Types of Weathering Mechanical/Physical Weathering processes that break a rock or mineral into smaller pieces without altering its composition Chemical Weathering processes that change the chemical composition of rocks and minerals

What is Mechanical/Physical Weathering? A rock is physically changed without a change in chemical composition Processes include: Frost Action / Ice Wedging Abrasion by wind and water Plant and Animal Action Thermal Expansion and contraction Pressure Unloading / Exfoliation

Frost Action / Ice Wedging Alternating freezing and thawing of water causes material to break up Example – Pot holes, Ice cubes in an ice tray Water expands between 4 and 0 degrees Celsius Volume increases by 9%!!!! The Bigger the crack gets, the more water it lets in……causing a snowball effect

Frost Action / Ice Wedging

Abrasion Wearing down or smoothing of a material due to constant collisions Example – Beach glass, sandblasting Breakdown caused by friction Rocks become rounded Waterfalls may result

Abrasions

Plant and Animal Action Plant root growth and uplift fracture rocks Animals burrowing also cause breakdown of rocks Actions also increase the exposure of rocks to air and water

Plant Action

Lichen (moss) on a rock or growth of tree out of the rock

Animal Action

Thermal Expansion and Contraction Extreme changes in temperature may cause cracking

Pressure Unloading / Exfoliation Cracking at weak joints due to a release of pressure Cause and effect of Exfoliation Rock breaks off into leaves or sheets along joints which parallel the ground surface Expansion of rock due to uplift and erosion removal of pressure of deep burial Occurs often in bedrock when glaciers recede

Exfoliation Peeling away of surface layers, caused by changes in temperature, pressure or vegetation (trees, grass, vegetation growing on rocks.) Roots wedge into pores and cracks, splitting the rock

Dome Exfoliation

What is Chemical Weathering? The Chemical composition of the rock is altered causing a change in properties Processes include: Hydrolysis Oxidation Acid Reactions / Carbonation

Hydrolysis Reaction of water with other substances Change is a very slow process Examples are: Feldspar  Kaolinite Anhydrite  Gypsum

Kaolin mine in Central Georgia

Where Oxygen combines with other substances to produce rust Oxidation Where Oxygen combines with other substances to produce rust Oxidation in the presence of water takes on a reddish- yellow brown color

Oxidation of basalt

Acid Reactions / Carbonation Carbon reacts with other substances to alter the chemical makeup of rocks Example: Carbonic acids (water + carbon dioxide) dissolve limestone which can results in the formation of underground caves Nitric acids produced by the decay of organic material can alter soil composition

Caves are formed when Carbonic Acid dissolves limestone

Stalactites (from the top) and Stalagmites (from the bottom) are formed in a limestone cave as a result of Chemical Weathering

Acid Rain has a drastic effect on rocks!

Nitric Acids in Soil When organisms or plants decay Nitric Acid is produced. This is absorbed into the soil and the chemical make-up of the soil has been changed.

Differential Weathering The variable rate of which rocks weather is called differential weathering Factors affecting the rate of weathering include: Composition (granite vs. limestone) Climate (hot, wet, cold, dry) Rock size (surface area)

Rocks weather at different rates due to. differences in mineral Rocks weather at different rates due to differences in mineral composition. The harder the rock, the slower the rate of weathering is. Some minerals are more Stable at the earth’s surface than others! These take longer to weather. Composition dictates hardness which determines resistance to weathering.

The climate that a rock is in is a factor in the rate of weathering. Cold Climates– mechanical weathering breaks down rocks rapidly Warm, wet climates – chemical weathering breaks down rocks rapidly

How much exposed area of the rock will also effect weathering In which shape will weathering occur faster?

EROSION/DEPOSITION The process of removing Earth materials from their original sites through weathering and transport agents or forces Transport Agents or Forces include: Water (Rain, streams, rivers, oceans, and ice/glaciers) Wind Gravity

Stream Erosion and Deposition

Streams

Glaciers

Wind Transport of Dust

Wind Transport of Dust

Gravity

Deposition Formations

Delta Formation from Deposition

Alluvial Fan from Deposition

What is the difference between Weathering and Erosion? REVIEW What is the difference between Weathering and Erosion? Weathering - processes at or near Earth’s surface that cause rocks and minerals to break down by air, water, plants and animals Erosion - process of removing Earth materials from their original sites through weathering and transport by water, wind or gravity

REVIEW- 2 Types of Weathering Mechanical/Physical Weathering - A rock is physically changed without a change in chemical composition Frost Action / Ice Wedging Alternating freezing and thawing of water causes material to break up Abrasion by wind and water Wearing down or smoothing of a material due to constant collisions Plant and Animal Action Plant root growth and animals burrowing increase the exposure of rocks to the air and water and causes breakdown Thermal Expansion and contraction Extreme changes in temperature causes cracking Pressure Unloading / Exfoliation Earth’s forces can push rock that formed deep underground up to the surface. The pressure causes the rock to expand and crack. This leads to exfoliation. Mechanical/Physical Weathering - In the natural process of mechanical weathering, physical forces split rocks apart but do not change their composition (like smashing a walnut).

REVIEW -2 Types of Weathering Chemical Weathering - Processes that change the chemical composition of rocks and minerals Hydrolysis Water is very slow reaction and the main cause of chemical weathering. Oxidation Where Oxygen combines with other substances to produce rust Acid Reactions / Carbonation Carbon reacts with other substances to dissolve and alter the chemical makeup of rocks forming caves. Nitric acid produced by the decay of organic material can alter soil composition

REVIEW (Continued) Differential Weathering - The variable rate of which rocks weather is called differential weathering. Most weathering occurs over long periods of time- hundreds, thousands, or even millions of years. Factors affecting the rate of weathering include: Composition (granite vs. limestone) What minerals a rock is made from Climate (hot, wet, cold, dry) hot, wet regions weather rocks faster than cold, dry ones Rock size (surface area) How large or small a rock’s surface is