Source: D4K: “Geology”
Visit the D4K companion Web site to learn more about Geology: D4K: “Geology”
This video segment from IdahoPTV's D4K describes the forces of earthquakes, volcanoes, water and glaciers that shape the surface of the earth. You see a fault line, Craters of the Moon lava fields, and examples of Idaho's batholith. Find out about tectonic plates and how they move. Discover the age and structure of the earth.
JOAN CARTAN-HANSEN: The earth is about 4.5 billion years old. It has an inner core of solid metal surrounded by a layer of liquid metal. Next is the mantle, a multi-layered collection of hot, heavy rock. The mantle is about 1,800 miles thick and on top is the rocky crust. That’s the part of the earth we see, the part we live on.
Geologists believe the earth was shaped by lots of different forces over periods of time and by studying the layers of rock and dirt and exploring the contours of the land, you too can learn how those forces shape the earth.
The surface of the earth is made up of bits of land known as plates. These plates are moving, sliding past one another, folding underneath or butting up against each other. When the pressure between two plates builds up to more than the rocks around them can stand, the plates crack and the energy is released in what we know as an earthquake.
CHILD: You can see why an earthquake can cause a lot of damage.
Put two wood blocks together and cover them with a layer of sand. Put a few buildings and animals on top and then move one of the blocks and that’s what an earthquake looks like!
JOAN: Earthquakes are most common where the plates meet. That’s known as a fault line and Idaho is number 6 on the list of states of most earthquakes.
A volcano is basically a hole in the earth’s crust where lava comes out. Lava is hot molten rock.
CHILD: Lava has viscosity. Some lava like this toothpaste comes out thick.
CHILD: Other lava like this ketchup comes out like a liquid.
Eventually, the lava cools into rock.
JOAN: Ancient volcanoes created the twisted landscape you see at craters of the moon national monument. In some parts of Idaho the mountains were formed when magma - or hot lave still underground – pushed upward but didn’t break the surface. That’s called a Batholith. These mountains are part of the Idaho Batholith.
a little bit of water can completely change a landscape. Over time moving water eats away at rock, so thousands of years later what was a plain can become a valley.
A flood can dramatically change the landscape. 15,000 years ago the Bonneville flood scoured out the Snake River plain, carving out the canyons at Twin Falls.
And not all floods are caused by nature. When the Teton dam broke in 1976, a wall of water almost wiped out many small towns including much of Rexburg.
CHILD: How fast the water can erode the land depends on how fast the water is flowing. A gentle flow doesn’t have much energy but a flood has lots of energy.
So the amount of damage to the land depends upon how much energy or force is involved.
JOAN: Glaciers are rivers of ice that carve their way through the land. They grow and push their way through creating ‘u’ shaped valleys with a flat bottom and high sides.
Even water in the form of rain can reshape the earth. Too much rain all at once can cause landslides. And even gentle rain and snow over time can wear away the top part of the earth showing the harder rock below. Freezing and thawing can also crack rocks open making it easier for water to eat away at the surface. Erosion, especially over time, can sculpt the land.
Water in all its different forms is one of the major forces that shape the earth. What forces carve the earth where you live?
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