Volcanic eruptions pull materials up from deep within the earth to form various volcanic landforms, such as lava domes, lava plateaus, fissure eruptions, craters and calderas. Learn about these volcanic landforms and how they are created.
Whether you are young or old, there is no doubt that volcanoes are pretty cool natural events – or should I say pretty hot events, since magma that forms under the earth’s crust can reach temperatures of around 2,000 degrees Fahrenheit?Magma is the hot molten rock that builds in pressure and explodes from the volcano as lava.
So a volcanic eruption is a way for the earth to blow off a little steam and at the same time pull materials from deeper layers of the earth to form new crust on the surface. The way a volcano erupts and the materials that make up the magma and lava of a particular volcano have a lot to do with the formation of the volcanic landforms, such as craters, calderas, lava domes and lava plateaus. Let’s take a closer look at these features and how they are formed.
Volcanoes come in all shapes and sizes.
Some volcanoes form majestic mountains, like Mt. Rainier in Washington State, and others have a very low, broad profile. The Hawaiian Islands are actually the tops of low-profile volcanoes that formed on the ocean basin.Still, most volcanoes share some similar features. For example, if we take a look inside a volcano, we notice it sits on top of a magma chamber, which is an area below the earth’s surface where magma gathers and builds in pressure. The magma chamber leads to a volcanic pipe, which is also called a volcanic conduit.
This is the passageway within a volcano leading from the magma chamber to the surface. At the surface, the magma, along with dissolved gases, exits the volcano through a vent.
The features of volcanoes are easy to remember if you relate them to the hot water heater supply in your house, whereas the magma chamber is like your hot water heater and the volcanic pipe is like the pipe that carries the hot water to your showerhead.
Of course, there’s always an exception to any rule, and we see that not all volcanoes erupt through a top vent; some volcanoes are nothing more than a crack in the earth’s surface. A fissure eruption is a volcanic eruption from a fracture in the earth’s surface rather than a volcanic vent. With a fissure eruption, magma finds its way to the earth’s surface through a crack in the ground.
This crack may be the result of the movement of tectonic plates, which are large sections of the earth’s crust. Since these plates meet at boundaries that are both on land as well as the ocean basins, we can see fissure eruptions under ocean waters.
As the magma seeps through cracks in the ocean floor, the lava hardens, helping to build underwater mountains and new segments of ocean floor.
On many volcanoes, there is a crater, which is a bowl-shaped depression at the top of a volcano caused by past volcanic eruptions. Craters can be thought of as the volcano ‘blowing its lid’ because it is where volcanic materials, such as ash, lava and rock fragments, are released.
A volcanic crater is relatively small, usually spanning about a half a mile in diameter or less, and can fill with water to form a crater lake.
As we mentioned, a volcano sits on top of a magma chamber. If a volcanic eruption causes the magma chamber to empty, the volcano can implode, forming a larger depression known as a caldera. So a caldera can be defined as a large volcanic crater formed by the collapse of the central part of the volcano.
You may have heard that Yellowstone National Park in the northwestern area of the United States is a site of past volcanic activity. In fact, many square miles of the park are actually a caldera called the Yellowstone Caldera.
This caldera is so large that it is hard to visualize the large depression, but it is a caldera that was formed by massive volcanic eruptions that occurred over the past 2.1 million years.
Lava Dome and Lava Plateau
The viscosity of the lava that erupts from a volcano can lead to the creation of different volcanic landforms.
If lava that erupts through a vent is highly viscous or thick, it will not flow very easily. This may result in a lava dome, which is a large, mound-shaped protrusion formed by viscous lava.
Because the lava is so thick, it cannot travel far from the vent and ends up being piled up on top of the volcano’s vent. It’s as if the volcano caps itself. However, this doesn’t mean the volcano becomes inactive.
In fact, lava domes can be unstable and cause the buildup of gases that leads to explosive eruptions.In contrast to the thick lava that creates a lava dome, we can see very runny lava come from a volcanic eruption. A lava plateau is a wide, flat surface formed when a large amount of highly fluid lava flows over an area. This thin and runny lava can disperse over large areas, and as the lava cools and solidifies, it forms the large, flat plateaus of rock.
Let’s review. Volcanoes come in all shapes and sizes, but most sit on top of a magma chamber that leads to a volcanic pipe or volcanic conduit, which is the passageway within a volcano leading from the magma chamber to the surface.
At the surface, the magma, along with dissolved gases, exits the volcano through a vent. A fissure eruption works a little differently. This is a volcanic eruption from a fracture in the earth’s surface rather than a volcanic vent.Many volcanoes have a crater, which is a bowl-shaped depression at the top of a volcano caused by past volcanic eruptions.
A volcanic crater is relatively small, usually spanning about a half a mile in diameter or less. A caldera is a large volcanic crater formed by the collapse of a central part of a volcano due to the emptying of the magma chamber below the volcano.If lava that erupts through a vent is highly viscous or thick, it will not flow very easily. This may result in a lava dome, which is a large, mound-shaped protrusion formed by viscous lava. In contrast, if the lava is runny, it might result in a lava plateau, which is a wide, flat surface formed when large amounts of highly fluid lava flows over an area.
When this lesson is done, you should be able to:
- Identify the various types of volcano landforms
- Explain how craters or calderas are formed
- Describe the difference between lava domes and plateaus