Matter flows within the Earth due to heat energy. That flowing energy can create volcanic eruptions as well as small and large earthquakes. These movements aren’t the only ways that change the Earth’s surface. Energy from the sun gives the power necessary to run the water cycle (which causes weathering and erosion) and produce winds. It also gives energy for the living organisms which helps to alter soil chemistry. With these two energy sources, Earth’s surface is dynamic, always changing.
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Mountain building processes through volcano activity and the folding of the Earth’s crust, work to build up the Earth’s surfaces. Sometimes layers of rock can become warped, folded, titled or even flipped upside down. The constant weathering of rock slowly works to break mountains down, create canyons, and even create underground caverns.
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Sometimes there are catastrophic changes to Earth’s surface features like landslides (see image of the 2001 El Salvador landslide above), tsunamis, volcanic eruptions, tornadoes or hurricanes. These phenomena possibly alter Earth’s surface extensively in very short periods of time, but most processes that make up Earth’s land formations are very, very slow.
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Take a look at the photos below of the Grand Canyon, Arizona. Grain by grain the Colorado river cut through what was once a flat plain. Slowly over the span of about 17 million years the Grand Canyon became the deep gorge it is today. As the river continues to flow, the canyon becomes deeper.
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If you look closely, you might notice that this isn’t all it took to create the Grand Canyon. In the photo below, you can see layers upon layers of rock. What you are seeing are sedimentary rock strata (layers) that formed horizontally at the bottom of a large ancient sea that is now long gone from this region. Nearly all of the layers of rock in the Grand Canyon are sedimentary rock strata that were deposited grain by grain, and then compacted and cemented over time dating back anywhere from 200 hundred million (top layers) to nearly 2 billion years ago (bottom layers).
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We once thought that the Earth was static, unchanging. We believed that mountains as they are, are as they were when the Earth formed. However, people began to notice little things like meandering rivers changing their course overtime. People thought about how much the land changed during an earthquake or landslide. After many observations and wondrous discoveries, we now know that the Earth is not static, but dynamic.
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You have probably noticed that mountains don’t just suddenly sprout out of the ground. Mountains seem so stable during a human lifespan, but mountains are a dynamic geologic feature that take about 100 million years to form, on average.
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Take Mount Everest for example. It is the highest mountain in the world at 8.85 km (29,029 feet) in elevation. So high in fact that climbers intending to get to the top need to have oxygen tanks just to stay conscious.
But did you know that at the top of many of the frozen peaks of the Himalayan Mountain range are fossils from an ancient sea? High up on the top of Mount Everest is a sedimentary rock that was laid down in the Ordovician age nearly 400 million years ago in the shallow Tethys Sea, which has long since dried up. The left photograph below is an image of an ammonite that lived in that sea. So how does a fossil like this one get to the highest point on the top of the tallest Mountain in the world? Very, very slowly.
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Earlier, we covered how the Earth was formed, and that there was heat energy in the Earth that is still left over from those violent beginnings. This heat energy doesn’t just make rock hot, it also moves it.
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As heat rises up inside the Earth it contacts the surface layer, and moves the surface in all sorts of directions. At some locations, the outer layer of Earth is moving in one direction while another part wants to push off in another. Since the outer layer of Earth is made of rock, it doesn’t bend and stretch very well. Pressures build up and then eventually the rocks fracture and you have an earthquake.
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The Himalayan mountains are similar to this example except the ground on either side of the mountain range is compressing into each other (see image below). These forces push rock up as the two sides collide, crumpling and folding rock. Eventually, these forces build a mountain between them (see diagram on the previous page). These compressional forces can be intense and sometimes cause violent earthquakes in the Himalayan range
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The Himalayas have been forming for about 50 million years and are still forming today. Compressional forces keep the ground on either side of the mountain range pushing into one another. When forces build up enough pressure to cause the rock to fracture, the mountaintop gets just a little bit higher. Small earthquakes might raise a mountain just an inch or two, but large earthquakes have been known to rupture and raise the ground surface 9 meters (29.5 feet) or more. With an elevation of 8.85 km or 8,850 meters, you can image that it has taken a very long time to build Everest into the peak it is today.
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So how did those fossils get there? Well, sedimentary rocks like limestone and sandstone aren’t very dense when compared to the more dense igneous rocks of the crust, and when two rock layers are pushed together, the denser rock layer will subduct (or go underneath the top layer). When the land masses were being pushed toward one another, sedimentary rocks like limestone and sandstone were already formed in the shallow sea basin. The land masses slowly moved in toward one another closing up the sea and eventually turning the low sea into a highland. Over a long period of time, the rocks that were formed at the bottom of the sea rose higher and higher until they made up the Himalayan mountain range.
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Landforms like mountain ranges and canyons take millions of years to drastically alter the landscape. That isn’t the case for volcanoes. The above figure shows a series of photographs of Mount St. Helens, located in Washington state. At the time of the first photograph, the active volcano had been rumbling for months. The North flank of the volcano (seen in the second image in the figure above) was swelling due to a shifting magma chamber. On the morning of May 18, 1980 a quake with magnitude 5.1 was detected coming from the volcano. In an unexpected turn, the North Flank of the volcano sloughed off the side of the mountain in just under 12 seconds becoming the largest landslide ever recorded.
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The grey eruption explosion soon followed, sending flows of hot gas and rock down the mountain with enough speed to uproot trees and strip them of their bark and branches. A huge plume of ash (pulverized rock) and gas shot kilometers into the sky. The animals and plants living there were killed in an instant. Fifty-seven people were killed in the blast as well.
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Eruptions like this one transfer a tremendous amount of energy from inside the Earth. This eruption was so powerful that it was equivalent to 1600 times the strength of the atomic bomb that was dropped on Hiroshima in the second World War. Nearly 40 years later, the forest closest to the volcano is still a barren landscape of bare trees lying where they fell. Further away from the base, life is returning to the region. Lupines, a type of flowering plant, bring color to the landscape and provide food for gophers. Elk and deer have returned to the land. Eventually, more life will return and trees will grow again, slowly returning the forest to its previous state until the next eruption.
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What energy source results in weathering and erosion?
Energy from volcanic eruptions.
Wind patterns from the atmosphere.
Energy from the sun drives the water cycle.
Heat from inside the Earth.
What causes movement beneath Earth's surface?
Gravity pulling soil down slopes.
Water filling cracks in rocks.
Heat energy causing rock to flow.
Wind pushing rocks around.
What happens to Earth's surface over time?
Natural forces only harm the surface.
It remains static and unchanging.
Humans prevent any changes from occurring.
It changes dynamically due to various forces.
What process builds up the Earth's surfaces ?
Sedimentation of soil
Weathering of rocks
Erosion by rivers
Mountain building
What happens to rock layers during Earth’s crust folding?
They can become warped and folded
They become completely flat
They disappear underground
They turn into lava
What effect does weathering have on mountains?
It breaks them down
It turns them into caves
It makes them taller
It freezes them in place
What are some examples of catastrophic changes to Earth's surface?
Ocean currents and tides
Landslides, tsunamis, and volcanic eruptions.
Wind erosion and rain
Earthquakes and droughts
What natural event can cause a landslide?
Heavy rainfall can trigger landslides on slopes.
Strong winds
Low tide
Sunny weather
What caused the Grand Canyon to deepen over time?
Wind erosion
The flow of the Colorado River
Earthquakes
Human activity
What river carved out the Grand Canyon?
Mississippi River
Amazon River
Rio Grande
Colorado River
What is the Grand Canyon primarily made of?
Grasslands
Sand dunes
Forests
Rock layers
What type of rock layers are found in the Grand Canyon?
Sedimentary rock strata
Metamorphic rock layers
Volcanic rock structures
Igneous rock formations
How were the sedimentary rock layers formed?
Formed from volcanic eruptions
Melted by lava flows
Carved by ancient glaciers
Deposited grain by grain over time
Where were the sedimentary layers deposited?
Inside a deep glacier
Above ground in deserts
At the bottom of a large ancient sea
On a volcanic mountain
What process helped form the sedimentary layers over time?
Melting and cooling
Freezing and thawing
Erosion by wind
Compaction and cementation
What natural events can change landscapes?
Earthquakes and landslides can alter landscapes.
Mountains never change.
Only floods can change landscapes.
Animals cause land changes.
How do rivers illustrate changes in the Earth?
Rivers can turn into mountains.
Rivers can change their course over time.
Rivers are always dry.
Rivers stay in one place forever.
What does dynamic mean in relation to Earth?
Earth changes only with humans.
Earth never changes.
Earth stays the same forever.
Earth is constantly changing over time.
How long does it take for mountains to form, on average?
Over 10 million years
About 100 million years
Several thousand years
A few hundred years
What type of fossil is shown in the left image?
Dinosaur fossil
Mammal bone
Ammonite fossil
Plant fossil
How old is the sedimentary rock containing the ammonite?
10,000 years
2 billion years
100 million years
Nearly 400 million years
What did the ammonite live in?
Forests
Shallow sea
Mountains
Deserts
What is still present in the Earth from its formation?
Water from oceans
Air trapped in rocks
Dust from space
Heat energy
What is a consequence of heat energy in the Earth?
Evaporation of water
Formation of clouds
Movement of rocks
Growth of plants
Why does the outer layer of Earth not bend easily?
It is too cold to bend.
It is covered by soil.
It is mostly liquid.
It is made of solid rock.
What can happen to different parts of the Earth's surface?
They can move in different directions.
They always move together.
They only go up and down.
They stop moving entirely.
How does heat affect the outer layer of the Earth?
It creates movement in the outer layer.
It cools the Earth's surface.
It causes rain to form.
It prevents earthquakes from happening.
What process creates mountains in this region?
Erosion of mountains
Spreading of tectonic plates
Melting of rocks
Compression of rock layers
What is likely to happen due to compressional forces?
Earthquakes may occur
Weather patterns will change
Volcanoes will form
Landslides will happen
How long have the Himalayas been forming?
About 50 million years
Since the dinosaurs
Less than 10 million years
About 20 million years
What happens when pressure builds up in mountain rocks?
Mountains become shorter
Rocks may fracture, raising the mountaintop.
Rocks collapse downwards
Rocks turn to liquid magma
Why does it take time to build Mount Everest?
Earthquakes happen too fast
It forms slowly over millions of years.
It's made of soft materials
It's constantly eroding
What type of rocks are less dense than igneous rocks?
Metamorphic rocks under pressure
Volcanic rocks formed underground
Igneous rocks from the crust
Sedimentary rocks like limestone and sandstone
What happens to the denser rock layer during subduction?
It melts into the mantle
It stays above the top layer
It breaks into smaller rocks
It goes underneath the top layer
What happens to rocks formed at the bottom of the sea over time?
They rise to form land features
They become igneous rocks
They stay at the seabed forever
They dissolve into the ocean
What was detected before the eruption occurred?
A significant snowstorm nearby.
Heavy rainfall in the area.
A landslide on the mountain.
A magnitude 5.1 earthquake.
What visual change was noticed on the North flank before the eruption?
It was getting covered in snow.
It was collapsing into the valley.
It was drying up from heat.
It was swelling due to magma.
What activity at the volcano preceded the climax eruption?
Total silence from the volcano.
Months of rumbling and seismic activity.
Clear, calm weather periods.
Frequent lightning storms nearby.
How did the volcanic eruption affect local wildlife?
Some animals escaped and survived.
Animals were unaffected by the blast.
Animals were killed instantly by the eruption.
Wildlife relocated to safer areas.
What is a significant feature of the eruption described?
The blast created a massive tsunami.
The eruption lasted for days.
There were colorful lights in the sky.
A huge plume of ash shot kilometers into the sky.
What caused the disruption in the area shown?
A volcanic eruption
A tornado
Human activity
Earthquake
What is the landscape like closest to the volcano?
Urban area
Barren landscape of bare trees
Lake with wildlife
Lush green forest
Which type of plant helps return life to the area?
Maple trees
Cacti
Lupines
Palm trees
What animal has returned to the land after the eruption?