Constructive & Destructive

Forces

EQ: What is the difference between a Constructive Force and a Destructive Force?

• Constructive Forces- Natural forces that build or construct landforms and cause changes in the Earth’s surface.

• Examples:– Volcanoes

– Deposition

– Earthquakes

Constructive ForcesConstructive Forces

• Constructive forces affect the earth's surface by building it up to form new landforms like mountains and islands.

• Examples of these type of forces are:• Deposition is the dropping off of bits of eroded

rock. This process helps to build up Earth’s surface by filling in depressions, or basins.

• Earthquakes• Volcanoes

• Destructive Forces – Natural forces that destroy landforms and causes damaging changes in the Earth’s surface. - Earthquakes– Weathering/Erosion

– Volcanoes

Earthquakes:

• Shaking that results from the movement of rock (tectonic plates) beneath Earth’s surface

• Destructive force or Constructive force

• Most occur because of moving crust

Earthquakes causes vibration across the ground, sending shock waves that crumble buildings.http://jclahr.com/alaska/aeic/taurho/eqeffects/eqtsun.mov

Stress:

• Force that acts on rock to change its shape and volume

• Energy is stored in the rock until it breaks or changes shape

3 Types of Stress:

1. Shearing – Pushes rock in opposite directions

past each other

- Transform boundaries

3 Types of Stress:

2. Tension – Stretches rock so that it becomes

thinner in the middle

- Diverging boundaries

3 Types of Stress:

3. Compression – Squeezes rock until it folds or

breaks

- Converging

boundaries

Faults:

• Break in Earth’s crust where slabs of crust slip past each other

• When stress builds up, the rock breaks along a fault

• Usually occur along plate boundaries

3 Main Types of Faults:

1. Strike-Slip – Rocks on each side slide past each other with little (or no) up & down motion

- Transform boundaries

- Caused by Shearing

- San Andreas (California)

Measuring Quakes:

• Seismograph –

• instrument used to measure the vibrations and seismic waves of earthquakes.

Rating Scales used for Quakes:

2. Richter – Rate quakes according to the size of the seismic waves

- low ---> high (1-9)

-each # is 10x stronger

- humans cannot feel a quake below 2

- 6 or more = major quake

- Measures magnitude

Misc. Info:

• Tsunami • – a series of seismic sea

waves- result from underwater

earthquakes, landslides, or volcanic eruptions

Best Way to Protect Yourself:Best Way to Protect Yourself:

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Volcanoes:• Destructive AND Constructive• Weak spot in the crust where molten

material from the mantle comes to the surface

• Magma – Hot molten rock located Below ground.

• Lava – magma that reaches the surface.

Volcanoes can quickly change the Earth, too, by pouring out hot, liquid rock called lava.

Pahoehoe

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Weathering:

• Process that breaks down rock & other substances at the Earth’s surface- very slow process

• Temperature, Water, & gases in the atmosphere all contribute to weathering

2 Types of Weathering:

1. Mechanical

2. Chemical

Mechanical Weathering:

• Process by which rock is physically broken into smaller pieces

• Small pieces have same material as the original rock

• Very slow occurrence

• The most common type of mechanical weathering is the constant freezing, and thawing of water. In liquid form, water is able to penetrate the many holes and joints within a rock. As the temperature drops water freezes and expands, becoming about 10% larger than it was in liquid form. The result is that the holes and cracks in rocks are pushed outward. Even the strongest rocks are no match for this force.

Rock split apart by Mechanical Rock split apart by Mechanical weathering.weathering.

Mechanical Weathering:• Caused by…(Agents)

– Freezing and Thawing– Release of Pressure– Growth of Plants

– Abrasion – Grinding away of rock by other rock particles that are

carried by water, ice, wind, or gravity

Chemical Weathering:

• Breaks down rock through chemical changes- Chemical properties are actually changed.

• Rock particles have different mineral make-up than original rock

Chemical Weathering:

• Caused by…(Agents)– H2O(Water) MOST important

– Oxygen (O2)

– Carbon Dioxide (CO2)

– Living organisms

– Acid Rain very rapid

Stalactites

Stalagmites

Stalactites & Stalagmites created by acid rain falling into these limestone caverns.

Agent Type DescriptionMechanical Rock particles wear away rock

Chemical Forms from coal, oil, and gas burning

Freezing/Thawing Breaks rock by ice wedging

Carbon Dioxide Forms carbonic acid in water

Chemical Weathers marble and limestone

Mechanical Burrowing in the ground breaks rock

Plant growth Roots pry apart cracks in rock

Living Organisms Produce weak acid that weathers rock

Oxygen Causes rust on some rock

Mechanical Sun or forest fire causes rock to crack

Erosion:• Process by which natural forces

move weathered rock & soil from one place to another (by wind, water, ice, & gravity)

• Sediment

•Material moved by weathering and erosion

Mass Movement:

• Deposition

• Caused by gravity

• Occurs where bits of rock are dropped off (deposited) because of erosion

• On land sediment can be moved down hill by:– Landslide– Mudslide

Landslide:

• Most destructive

• When rock & soil slide quickly down a steep slope

Mudslide