Impact of Natural Events

Impact of Natural Events

Ecoregions

• An ecoregion is an ecosystem that covers a large area.

• An ecosystem is a community of organisms and their nonliving environment.

• Within an ecoregion, the climate and plant life are similar.

• Texas has 6 types of ecoregions: coastal prairies and marshes, plains, prairies, woodlands, plateau, and desert/montane woodland.

Multiple Choice

Calculate: Scientists estimate that the Blackland Prairies originally consisted of approximately 20,000,000 acres. If only about 5,000 acres of the original Blackland Prairies remain, what percent of the original acreage exists today?

• 2.5%

• .25%

• .025%

• .0025%

Changes in Ecoregions

• Natural processes, such as weathering, erosion, and deposition, are constantly changing the environment within ecoregions.

• Weathering breaks down rock into smaller pieces. It may be caused by water, wind, cycles of heating and cooling, and acids in rain.

Changes in Ecosystems Continued...

• Erosion is the movement of material. It causes pieces of weathered rock or topsoil to move from one location to another. Wind, water, and gravity can cause erosion.

• Deposition is the laying down, or depositing of eroded material. For example, deposition takes place at the mouth of a river where sediments carried by the moving water are dropped.

Multiple Choice

Calculate: If 32,000,000 acres in Texas are cropland and 40 percent of that cropland is considered highly erodible, how many acres are highly erodible?

• 80,000,000 acres

• 19,200,000 acres

• 12,800,800 acres

• 6,400,000 acres

Chemical Weathering

• Chemical weathering occurs when water dissolves minerals in a rock, producing new compounds. This reaction is called hydrolysis.

• For example, water interacts with calcites in caves, causing them to dissolve. Calcite in dripping water builds up over many years to create stalagmites and stalactites.

Stalagtites and Stalagmites are examples of chemical weathering with water.

Oxidation

• Another type of chemical weathering works on rocks that contain iron. These rocks turn to rust in a process called oxidation.

• Rust is a compound created by the interaction of oxygen and iron in the presence of water. As rust expands, it weakens rock and helps break it apart.

Rocks that contain iron turn to rust when exposed to oxygen and water.

Acid Rain

• Certain kinds of air pollution increase the rate of weathering. Burning coal, natural gas, and petroleum releases chemicals such as nitrogen oxide and sulfur dioxide into the atmosphere.

• When these chemicals combine with sunlight and moisture, they change into acids. They then fall back to Earth as acid rain.

• Acid rain rapidly weathers limestone, marble, and other kinds of stone. The effects of acid rain can often be seen on gravestones, making names and other inscriptions impossible to read.

Old gravestones are often an example of chemical weathering with acid rain.

Karst

• Limestone, also known as chalk or calcium carbonate, is a soft rock that dissolves in water.

• Sometimes, chemical weathering dissolves large portions of limestone or other rock on the surface of the Earth to form a landscape called karst.

• In these areas, the surface rock is pockmarked with holes, sinkholes, and caves.

• One of the world’s most spectacular examples of karst is Shilin, or the Stone Forest, near Kunming, China. Hundreds of slender, sharp towers of weathered limestone rise from the landscape.

One example of a karst landscape can be found at Shilin, or Stone Forest, near Kunming, China.

Physical Weathering

• also known as Mechanical Weathering and disaggregation

• ...causes rocks to crumble

• Examples of physical weathering include frost weathering, thermal stress, and salt weathering (haloclasty).

Freeze-Thaw Cycle

• Water, in either liquid or solid form, is often a key agent of mechanical weathering.

• For instance, liquid water can seep into cracks and crevices in rock. If temperatures drop low enough, the water will freeze. When water freezes, it expands. The ice then works as a wedge. It slowly widens the cracks and splits the rock.

• When ice melts, liquid water performs the act of erosion by carrying away the tiny rock fragments lost in the split. This specific process (the freeze-thaw cycle) is called frost weathering or cryofracturing.

Thermal Stress

• Temperature changes can also contribute to mechanical weathering in a process called thermal stress.

• The outer layer of desert rocks undergo repeated stress as the temperature changes from day to night.

• Eventually, outer layers flake off in thin sheets, a process called exfoliation.

Salt Weathering or Haloclasty

• Salt also works to weather rock in a process called haloclasty.

• Saltwater sometimes gets into the cracks and pores of rock.

• If the saltwater evaporates, salt crystals are left behind.

• As the crystals grow, they put pressure on the rock, slowly breaking it apart.

Biologic Weathering

• Biological weathering can be caused by plants or animals.

• The seed of a tree may sprout in soil that has collected in a cracked rock.

• As the roots grow, they widen the cracks, eventually breaking the rock into pieces.

Catastophic Events

• Catastrophic weather events include hurricanes, tornadoes, blizzards, and droughts, among others.

• Tropical cyclones are the most costly of the weather and climate disasters.

• Since 1980, the U.S. has sustained at least 285 weather and climate disasters. The total cost of these 285 events exceeds $1.8 trillion.

In the U.S., catastrophic events include flooding, blizzards, wildfires, drought, earthquakes, and tornadoes.

Tropical cylcone or hurricane approaching the Greater Antilles of the Carribean.

Poll

Have you ever survived a catastrophic event?

• Yes, I have.

• No, I haven't.