Internal & External Forces

<aside> 💡 From this section, you must know…

  1. What is the sphere that all living things inhabit?
  2. What are the internal forces in the lithosphere and how do they affect life on Earth?
  3. What are the external forces that shape Earth’s surface? </aside>

All of the forces that change the Earth’s surface are known as physical processes.

<aside> ☝ Definition: Physical Processes - Gradual changes through a series of events of the Earth

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Geographers study the physical processes and interactions among four physical systems – Earth’s atmosphere, lithosphere, hydrosphere and biosphere. While we are developing a better understanding of how these systems interact with one another, we are far from being able to predict and purposefully change them.

<aside> ☝ Definition: Lithosphere - the earth’s crust and uppermost mantle

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Internal Forces

Internal forces are all of the forces that shape the Earth’s surface beneath the lithosphere.

The most important internal force to consider is the movement of the tectonic plates. Tectonic plates are enormous moving pieces of Earth’s lithosphere. All major continents and subcontinents sit on their own tectonic plates.

Video: The Ring of Fire

https://www.youtube.com/watch?v=DrwYtGf40hA&pp=ygUQcmluZyBvZiBmaXJlIHZveA%3D%3D

The Ring of Fire is a region of the world with very high seismic activity. Forming a ring around the edge of the Pacific Ocean, the tectonic plates in this area move faster, creating more pressure than normal. This leads to more frequent earthquakes and volcanic eruptions.

While seismologists can analyze tremors, gases, and magma activity to predict volcanic eruptions, earthquakes are impossible to forecast.

Types of Interactions Between Tectonic Plates

Convergent Boundary Subduction Boundary Divergent Boundary Transform Boundary
Where plates collide into each other Where one plate goes under another Plates move away from each other Plates slide past one another
Mountains
For example,
The Rocky Mountains Volcanoes and earthquakes
Ex: Chile, South America Rifts, valleys
Ex: The Great Rift Valley, Africa
Earthquakes
Ex: San Andreas Fault, California

External Forces

External forces are the processes that happen outside the earth’s crust that change the land.

| Water Erosion | Weathered material is moved by water, such as rivers and waves.   Rivers will eventually carve a canyon into rock sediment. Valleys may also form this way. This may take years or decades, depending on the type of rock. | Responsible for: rivers, canyons, coastal erosion | | --- | --- | --- | | Wind Erosion | Weathered material is moved by wind.   By blowing away topsoil/sand, wind erosion may create desertification and sand dunes. | Sand dunes, desert (along with climate) | | Glacial (ice) movement | Weathered material is moved by moving or melting glaciers. | All kinds of terrain | | Weathering | Weathering is the breakdown of materials into smaller pieces Mechanical Weathering breaks rocks into smaller pieces by forcing them apart. This can be done with ice forming or tree roots. Chemical Weathering breaks rocks by eating away at them (changing composition) with chemicals in the air or water. | |