shaping, carving, and wearing landforms Weathering and Erosion

Transcription

1 shaping, carving, and wearing landforms Weathering and Erosion

2 Weathering and Erosion drive the rock cycle Weathering process of breaking down materials (rock and minerals). Erosion process of moving sediments from one place to another, usually by wind, water, gravity, or a combination of these forces. Given enough time, weathering and erosion can transform the land by carving valleys, tearing down cliffs, and flattening mountain ranges. 2

3 How do you know if a rock is being weathered? Does it look like its starting to crumble?...have cracks?...color changing?...how is this happening? Types of Weathering: Mechanical Weathering Chemical Weathering - The substance undergoes a physical change. - Process of physically breaking down materials without altering the chemical composition of its components. - The substance undergoes a chemical change. - Process that changes materials by altering the chemical composition of its components 3

4 Hinge Point Questions: How are weathering and erosion different? Weathering is the process of breaking down rock and minerals while erosion is the process of moving sediments from one location to another. What are some signs of weathering? Does the material look like it is going to crumble? Does it have cracks? Is the color changing?

5 Mechanical Weathering Physically breaking or wearing down the parent material into smaller pieces without changing them chemically. A PHYSICAL CHANGE Parent material can disintegrate, but not change is composition. TYPES Abrasion Freezing and Thawing Living Organisms Exfoliation

6 Freezing and Thawing: Mechanical Weathering Water gets into cracks in rock, the water freezes, it expands and the outward force widens the cracks. The water thaws, the cracks can refill and continue the process. Over time, this process acts as a wedge, slowly widening the crack until it breaks the rock apart. Ice Wedging most often occurs in regions of constant freeze and thaw cycles in late winter and early spring. Examples: potholes in roads to giant cracks in a slab of rock on a cliff.

7 Freezing and Thawing: Mechanical Weathering

8 Abrasion: Mechanical Weathering Occurs when rock is gradually scraped and sanded down by particles carried by water, wind, or ice. Sediment carried by flowing water can collide and gradually grind away rocks in a streambed. Sediment can be carried by wind or slow moving glaciers Overtime, this sediment can carve and shape the land. GLACIERS RUNNING WATER WIND

9 Exfoliation: Mechanical Weathering Occurs when outer layers of rocks flake off caused by changes in pressure or temperature due to the expansion or contraction of rocks. When rock expands after a massive weight is removed. Glaciers recede and rock no longer has compression. Rocks in daily temperatures with large changes undergo exfoliation. Hot during the day and cold at night, daily cycle of expansion and contraction.

10 Living Organisms: Mechanical Weathering When living organisms cause rock to weather and break apart. Tree roots grow into cracks of rocks, widening the cracks as the tree grows. Animals burrow (moles, gophers, and insects) and can loosen and break apart rocks in the soil. Living organisms played a critical role in revitalizing the Mt. St. Helens region after the 1980 eruption. Gophers that survived the eruption deep underground helped to mix the ash, soil, and rock, distributing nutrients in the soil evenly allowing the conditions to be suitable for life.

11 Hinge Point Questions: Identify and describe 3 of the 4 examples of mechanical weathering. Ice Wedging Freeze and thaw of water in cracks. Abrasion Carve and polish rock by wind, water, and ice. Exfoliation Outer layer of rock flakes off by compression and/or heating differences. Living Organisms Trees grow in cracks/animals burrow mixing soil How can heating and cooling cause weathering? As the rock is heated it expands, then contracts as temperatures drop. This expansion and contraction can cause the outer layer of rocks to flake off.

12 Chemical Weathering Occurs when chemical interactions change the chemical structure or composition of minerals within a rock, breaking down the rock. TYPES A CHEMICAL CHANGE Oxidation Hydrolysis Living Organisms Carbonation

13 Oxidation: Chemical Weathering Commonly known as rusting occurs when rocks and minerals are exposed to oxygen, reacting with certain minerals and changing their chemical composition. Accelerated in environments of high moisture and temperature. Rocks containing iron (Fe) oxidizes when exposed to oxygen producing iron oxide (Fe 2 O 3). This causes the rock to weaken and crumble easily.

14 Hydrolysis: Chemical Weathering Occurs when minerals react with ions, such as hydrogen (H + ) from water. When it rains acidic water comes into contact with silicate minerals to form new minerals. This causes larger rocks to break into smaller pieces or to change into silts or clays. June 27,

15 Carbonation: Chemical Weathering Occurs when carbon dioxide (CO 2 ) dissolves in water (H 2 O), forming carbonic acid (H 2 CO 3 ). This process occurs naturally in the atmosphere creating acid rain. When acid rain falls on and seeps into the cracks of rocks rich in minerals that react with acids (calcite - CaCO 3 ), it will break down the rock. The effects of acid rain can be seen in many old buildings, statutes and tombstones that were constructed using limestone and marble, which are both rich in calcite. June 27,

16 Living Organisms: Chemical Weathering When living organisms secrete a weak acid that dissolves some of the minerals in the rock. The dissolved minerals provide the organism with some of the nutrients that help them grow.

17 Hinge Point Questions: Describe some evidence of chemical weathering. In chemical weathering, the might experience a change in color of the rock, a substance growing on the rock, or a new substance being created. How is acid rain produced. Atmospheric carbon dioxide mix with water vapor to produce a weak acid when it rains.

18 Rates of Erosion Environmental conditions constantly bombard rocks at different intensities, affecting the rates at which they weather. Weathering is a gradual process that occurs over hundreds, thousands, and even millions of years. There are 5 factors that affect the rate of weathering. Type of Rock Surface Area Human Activity Exposure Climate

19 Rates of Erosion Type of Rock Surface Area Exposure Each type of rock (igneous, sedimentary, and metamorphic) have a unique set of physical properties. Igneous rock like granite will weather slower than softer rock like sandstone, and sandstone will wear away slower than limestone in a wet environment. The greater the surface area exposed to an erosional agent, the faster it will weather. Overtime, the amount of the rocks surface area will increase, increasing the rate of weathering. This process compounds over time eventually breaking down the rock. Uncovered rocks will generally weather faster than covered rocks (soil, water, or ice). Example: A large boulder that is mostly buried may not weather as quick as a small rock that is lying on top of the ground.

20 Rates of Erosion Climate Human Activity Climate is a combination of temperature, humidity, rainfall, and sunlight at a given region on Earth. Different combination of these factors will affect the rate at which rock weathers. Hot and Humid conditions accelerate oxidation of rocks containing iron. Large variations in temperature can cause exfoliation. Regions of heavy precipitation will weather sedimentary rock (sandstone) faster than dryer climates. The biggest influence on weathering rates. (ie: clearing lands construction) What might take millions of years to naturally break down might take a only days due to human activity. EXAMPLES: Landscaping/agricultural practices Mining Clearing forest/trees Industrialization also affects weathering rates - greenhouse