There are many geologic processes that shape the surface of the Earth. Not only do they build and destroy a variety of landscapes, but they also give us clues to the interior of the Earth and the forces that exist there.
The Dynamic Earth
If you have ever been to Hawai’i, you may have had the opportunity to snorkel. People are attracted to this activity because it gives you a small glimpse of the interesting features of the Earth that we often miss out on by living above water.
Identifying these features both underwater and on land can give us some clues as to how the lithosphere, or the Earth’s crust, changes.Hawai’i is a great place to observe these changes because, unlike many places, they all can occur there. Just like snorkeling gives us a glimpse of what happens under the waves, volcanoes and earthquakes can give us glimpses of what is happening under the lithosphere, inside the Earth.
Volcanoes and earthquakes are natural disasters that can radically transform the landscape of the Earth in just a few moments. This, along with the ongoing breakdown of the surface of the Earth by weather, produces profound changes over time over the world.
However, they have found that after an earthquake, waves of energy travel not only through the rocks of the Earth’s surface but also through the center of the Earth. The waves that pass through the Earth travel at different speeds depending on the rock type, its temperature, and its pressure.
Following an earthquake, scientists at stations all around the Earth record the time and intensity of the waves that arrive at their location. Using information about the arrival and behavior of the waves, scientists can deduce a picture of the different layers of the Earth’s interior. This is how scientists have developed a 5-layer model of the Earth consisting of a solid inner core, a liquid outer core, a liquid mantle, a taffy-like upper layer, all underneath the outer crust.
Tidal waves, or tsunamis (as shown in this animation), are also the result of earthquakes, and they can affect land, including the islands of Hawai’i. Tsunamis can form in a couple of ways.
One, an earthquake could trigger a massive landslide near a body of water. This landslide entering the water could trigger a large wave similar to the waves made when someone jumps in the pool. The mass of the material entering the water triggers the wave.
Out in the open ocean, the tsunami may not look like much, usually having a long, low crest, but these waves can move quite fast, up to 500 miles per hour. As the wave reaches the shoreline, it begins to slow down and pile up on itself. Initially, the shoreline water of the ocean may recede from the shore as it gets pulled into the wave itself. Tsunamis also may occur in several waves, increasing the danger of the event. Tsunamis have so much energy that they push up on land like a bulldozer, causing massive destruction.
Volcanoes and Hot Spots
Volcanoes are formed one of three ways. First, magma can ooze out of the ground when the lithosphere pulls apart. These are often non-explosive volcanoes that form where two pieces of the Earth are pulling apart. Second, volcanoes can erupt explosively, usually the result of a piece of the Earth’s crust being forced back into the mantle. The piece of crust re-melts and moves to the surface to cause the eruption. The third way a volcano can be formed is called a hot spot.
Deep inside the Earth, hot magma moves toward the surface of the Earth the way bubbles move in a pot of boiling water. These isolated columns of magma are known as mantle plumes, and when they reach the crust of the Earth, they break through in one spot, forming an area of volcanism. Yellowstone National Park and the Hawai’ian islands are hot spots, examples of volcanic activity caused by these rising mantle plumes. This activity can be seen in Yellowstone’s hot springs, geysers, and leftover volcanic deposits.Over long periods of time, the hot spots are relatively stationary, so as the plates move over it, chains of islands can be produced. Hawai’i is a prime example of this.
The Hawai’ian islands were created one at a time over long periods. The furthest northwest island is the oldest, and the Big Island of Hawai’i is directly over the hot spot. The Big Island is the site of Kilauea, where most of the volcanic activity is found. Off the Big Island’s southeast coast, a new island is forming deep under water, but it will be a long time before the new island of Lo’ihi breaks the surface.
Studying the types of lava that come out of volcanoes also gives scientists some clues about the Earth’s interior.
Weathering and Deposition
On the surface of Hawai’i, two other processes are really evident. These processes are known as weathering and deposition. Weathering is the wearing away of rock by wind, water, or any other natural agent. This could include repeated heating by the sun or cracking of rocks by water that expands when frozen.
This can be seen in this image, which shows drainage channels on either side of the main valley. These are formed from water running off from heavy rainfall.Deposition is where sediment and other broken-down parts of rocks accumulate to create landforms. Weathering and deposition are opposites of each other and are part of a process that changes the Earth’s landscape due to climactic factors. Evidence of weathering can be seen in these pictures. As the volcanic rocks of Hawai’i are eroded and washed into the ocean, they often get deposited on the beaches by waves. This is what causes the famous black sand beaches found there.
There are many processes and events that shape the Earth’s surface and also give us clues about the Earth. Earthquakes show us the power that can be released through pieces of the Earth’s crust moving, which creates faults, cracks in the Earth’s crust that show movement. Scientists can monitor the arrival of earthquake waves at different points on the Earth, allowing them to build a model of the Earth’s interior and deduce how earthquakes are caused.Tsunamis are rapidly moving, destructive tidal waves that are most commonly caused by underwater earthquakes. The water piles up as it reaches the shore and acts like a flash flood, causing massive destruction.Oftentimes, volcanoes are the result of pieces of the Earth’s crust moving around, but hot spots, formed by mantle plumes in the Earth’s interior, push through the crust creating a volcanic zone. The lava and detritus that volcanoes emit during an eruption give us a glimpse of the interior of the Earth.The surface processes that change the Earth include weathering – the wearing away of rock by natural processes, erosion – the movement of broken down rock, and deposition – where the pieces of broken rock end up being placed.
After watching this lesson, you should be able to:
- Explain how seismologists can map the inner layers of the Earth
- Understand how faults, tsunamis, earthquakes, and volcanoes can occur
- Define mantle plume, weathering, erosion, and deposition