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Geology: Top 10 Questions

January 2012

Thanks to Reed Lewis, Geologist, Idaho Geological Survey, University of Idaho; and Megan Dixon, Adjunct Instructor, College of Idaho for the answers.

1: What type of rock is the Capitol made out of?

It's made out of sandstone. In Idaho, there were great deposits of sand that formed into sandstone over a long period of time. The material that was in the water over the years helps to hold the sandstone together and adds to the beauty of the buildings. (From Luke in Mrs. Schweitzer's class at Riverside Elementary School in Boise)

2: How do people make sand so soft and in so many pieces?

Most of the sand is not made by people, but by the weathering of rock. Freezing and cooling of rock, along with water washing it down into streams and beaches, form sand. (From Madison in Mrs. Woodall's class at Dalton Elementary School in Dalton Gardens)

3: Statues are made out of rock and look like one giant rock. How do people make statues that look like a single piece of rock?

When people make statues, they look for rock that has accumulated into one large mass. Marble is often used to make statues. Marble is found in special places and in big pieces, so there are statue-sized pieces of marble. (From Renee in Mrs. Woodall's class at Dalton Elementary School in Dalton Gardens)

4: If weather can break a rock, can it break a crystal rock?

Weathering can also break crystals, but it will take longer than breaking a rock. Crystals are pure sheets of a single grain of mineral and they don't break up as easily as rock. (From Ally in Mrs. Woodall's class at Dalton Elementary School in Dalton Gardens)

5: Is Yellowstone a super volcano that's ready to explode at any minute?

Yellowstone is a caldera, a collapsed area where there is some action under the crust. Will it erupt at any minute? Probably not, but it is watched very carefully. There is a prediction that something will happen in the future. It's all dependent on the amount of pressure that builds up under the crust. (From Austin in Mrs. Hunt's class at Cynthia Mann Elementary School in Boise)

6: Does the earth grow?

Yes, but it depends on what you mean by growing. There are areas that are mostly under the ocean (but not always) where lava is coming up to the surface and pushing. You could say the earth is growing at that point because this spreads the earth's crust. When you have lava coming to the surface and cooling, you could say the earth is growing because the lava forms into crust, which increases the surface of the earth. (From Grace in Mrs. Durham's class at Hayden Meadows Elementary School in Coeur d'Alene)

7: How do mountains form?

Mountains form in different ways. Some mountains, like the Cascades, form by lava coming out of the crust and flowing out onto the surface. Mountains can also be formed from erosion. Over time, water washes over materials and forms canyons and mountains. Many mountains in Idaho were formed this way. A third way is when you have a combination of water moving and material coming out. With this way, there is a fault at the base of a peak, which drops the valley down and brings the mountain up. A fourth way is when continents collide into each other causing the crusts to get smashed together and stay on top of one another. The Himalayas were formed this way. (From Hope in Mrs. Hunt's class at Cynthia Mann Elementary School in Boise)

8: Why are minerals different colors?

The elements in minerals give the minerals their color. For example, a little bit of chrome may cause a mineral to be green. Iron may cause a mineral to have red tones. (From Taylor in Mrs. Woodall's class at Dalton Elementary School in Dalton Gardens)

9: What would happen if a man went to where the earth's crust was finished, and dig?

If you go too far down, you'd get melted along with your equipment, or crushed by the pressure of the rock. There are places where the crust is thinning and you don't have to go too far. If you go to a place where there is lava, like on the islands of Hawaii, the crust is thinning or there is a gap for the lava to escape to the top. Here, you wouldn't want to dig too far because you would reach the mantle and that heats up very well. (From Gabriel in Mrs. Durham's class at Hayden Meadows Elementary School in Coeur d'Alene)

10: What are the chances of having another earthquake?

Excellent! We don't know when, but geologists have spent a lot of time trying to predict the next earthquake. We've made progress, but fundamentally, they tend to be a surprise. Major earthquakes draw our attention, but earthquakes are happening every day. We just don't feel all of them. (From Gus in Mrs. Schweitzer's class at Riverside Elementary School in Boise)


September 2009

Thanks to Scott Hughes, Dean of the College of Arts and Sciences, Idaho State University; and Matt Kohn, Associate Professor of Geology, Boise State University for the answers.

1: How are rocks formed?

As the planet heats up, it undergoes the process of differentiation. This is where it begins to partially melt and the core forms out of this material that sinks deeply. Then, the crust floats up to the surface. These very first rocks are igneous rocks. Once these rocks become subject to change, they become metamorphic. At this point, if there is a surface process that can alter them chemically, causing erosion, transport and deposition, they become sedimentary rocks. Rocks basically start from an igneous state and get transformed from there. (From Taylor in Mrs. Schweitzer's class at Riverside Elementary School in Boise)

2: How are caves formed?

Caves are normally formed by surface water that penetrates down into limestone or a material that's made of calcium carbonate. Normally, water that percolates into the earth is slightly acidic, similar to baking soda. If you add acid, it will dissolve away holes in the limestone leaving a cave. (From Zach at McDonald Elementary School in Moscow)

3: How can you tell if you have real gold?

Real gold is very soft and dense. It's easy to scratch. However, even though fool's gold is gold colored, it's actually iron sulfide and is much harder than gold. You can't deform fool's gold like you can real gold. (From Kirsten in Mrs. McCoy's class at Donnelly Elementary School in Donnelly)

4: Why do crystals look so shiny and pretty?

Crystals have underlying structures, so they tend to break in certain ways or to form faces. They look shiny because the faces reflect the light. When we look at a crystal, the reflection lets us see the underlying structure. (From Marissa in Mrs. Drainsfield's class at Mary McPherson's Elementary School in Meridian)

5: What minerals are found in Idaho?

There's a lot of volcanic rock that has minerals, white crystals and green crystals. Idaho is famous for having certain kinds of garnets. You can find star garnets near Moscow. (From Jayce in Mrs. Childers' class at Hayden Meadows Elementary School in Hayden)

6: Is there any rhyme or reason to when volcanoes go off?

It depends on how the magma comes into the volcano. If there is a lot that comes in at a particular time, it will erupt more frequently. In general, the way the magma comes in is quite chaotic, so there is no way of predicting a volcanic eruption way in advance. (From Jasmine in Mrs. Schweitzer's class at Riverside Elementary School in Boise)

7: Can an earthquake break lands apart?

An earthquake can break the surface of the earth, but if there is any spreading where the lands starts to pull apart, it is almost immediately followed by a collapse which sort of brings it back together. So, an earthquake does not open up with big cracks and swallow people up. Instead, an earthquake allows the surface to reconstruct itself changing the surface of the earth. (From Alexa in Mrs. Tanner's class at Hayden Meadows Elementary School in Hayden)

8: How are diamonds formed?

Diamonds are actually pieces of carbon. When carbon is put under high pressure and high temperatures (somewhere between 50-150 miles beneath the surface of the earth), it will form molecules that are so tight that the crystal structures become the hardest known to humans. These are diamonds, and they get to the surface by being erupted through a volcano. (From Ethan in Mrs. Boehne's class at McDonald Elementary School in Moscow)

9: What's the most rare kind of rock found?

The most rare rock found is a meteorite from Mars. (From Kate in Mrs. Hunt's class at Cynthia Mann Elementary School in Boise)

10: How long does it take to make a valley more than a thousand feet deep?

A valley that is a thousand feet deep could take between 10,000 to 500,000 years if the rock is very resistant to erosion. If the rock is very resistant and strong, and the forces are very slow, it could take thousands or even millions of years. But, if the rock is very loose, like sand, and the water is running fast, it might take only a few weeks to form. (From Annika in Coeur d'Alene)


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