DestructiveForces

S5E1 Students will identify surface features of the Earth caused by constructive and destructive processes. b. Identify and find examples of surface features caused by destructive processes.Erosion (waters-rivers and oceans, wind)WeatheringImpact of OrganismsEarthquakeVolcano

Created for TCSS

Weathering Weathering is the process of

decomposing, breaking up, or changing rocks. Weathering may be caused by the action of water, air, chemicals, plants, or animals.

There are two main types of weathering – physical (mechanical) weathering and chemical weathering.

Click here to view examples of weathering.

Weathering must occur BEFORE erosion can happen.

WeatheringPhysical weathering, also called

mechanical weathering, is the process of breaking a large rock into smaller pieces without changing the minerals in the rock.

Physical weathering can occur in a number of ways. Water, wind, and temperature changes are the main causes of physical weathering.

WeatheringChemical weathering involves

chemical changes in the minerals of the rock, or on the surface of the rock, that make the rock change its shape or color.

Chemicals in the air mix with water to make acid rain that eats away at limestone rock.

Oxygen reacts with iron and forms rust.Chemical weathering can occur when the

acid in ground water begins to wear away at the limestone, leading to the formation of a cave.

Erosion

Once the small pieces of rocks are changed or broken apart by weathering, they may start to be moved by wind, water, or ice. When the smaller rock pieces (now pebbles, sand or soil) are moved by these natural forces, it is called erosion.

So, if a rock is changed or broken but stays where it is, it is called weathering. If the pieces of weathered rock are moved away, it is called erosion.

Click here to view examples of erosion.

Impact of OrganismsBelieve it or not people, animals, and

other organisms are constantly eroding the earth around them. Often times it is just a little bit of dirt sliding off a walking path but other times it can lead to massive problems.

During the Great Depression in the 1930's poor farming techniques helped cause what we now call the “Dust Bowl”. Lichens

growing on rock produce weak acids that slowly dissolve rock.

Tree roots in rock, Anna Ruby Falls, GA

Animals dig in the soil and loosen and break apart rocks.

Earthquakes

Earthquakes can be both a constructive and destructive force. They occur on faults within bedrock. When the fault lines move they become a destructive force and often cause incredible damage.

Click here to watch a video clip about earthquakes.

VolcanoesVolcanoes are mountains with

openings in Earth’s crust through which magma, gases, and ash reach Earth’s surface. Volcanoes can change Earth’s surface. When the magma erupts from the volcano the top of the mountain can be changed. The lava and ash can destroy forests and bury fields.

Click here to watch a video clip about a volcano’s destructive force.