Shield volcano

A shield volcano is a big mountain.

It looks like a shield lying on the ground.

This shape happens because the lava is very runny. The lava flows far away from the top. It builds up in wide, thin layers over a long time. This makes the mountain very wide and flat. These volcanoes can be huge. Some are even on other planets like Mars.

They are some of the largest volcanoes on Earth.

A shield volcano is a type of volcano. It has a low profile. It looks like a shield lying on the ground.

This shape happens because of the lava. The lava is very fluid. This means it is thin and runny. It can flow a long way from the top.

Over a long time, many thin layers build up. This makes the volcano very wide and broad.

These volcanoes can be very big. Mauna Loa in Hawaii is one of the largest on Earth. It is so heavy that it pushes down the crust.

You can even find giant shield volcanoes on other planets. Olympus Mons on Mars is a great example.

Lava flows can look different. Some lava is smooth. We call this pāhoehoe. Other lava is thick and blocky. We call this ʻaʻā. Some lava flows through lava tubes. These are cave-like paths. The walls of the tube keep the lava warm. This helps the lava flow even further.

A shield volcano is a special kind of volcano. It has a low profile that looks like a shield lying on the ground.

These volcanoes are different from other types because of the lava they erupt. They erupt lava that is very fluid, which means it is thin and runny. This runny lava can travel a very long distance before it cools down. As it moves, it forms thin sheets of rock. Over a long time, these layers build up to make a wide, broad shape.

The way a shield volcano grows is a slow and steady process. Most eruptions are gentle and called effusive eruptions. Instead of huge explosions, the lava flows out smoothly from vents. Sometimes the lava comes out of a long crack called a fissure. This can create a "wall of fire" that looks like a long curtain.

The lava can also move through lava tubes. These are cave-like paths that keep the lava warm so it can flow further. About 58% of the lava at Kīlauea comes from these tubes.

Scientists have studied these volcanoes for a long time. The name comes from a German word, "Schildvulkan." An Austrian geologist named Eduard Suess first used this term in 1888. By 1910, the name was used in English. Much of what we know comes from studying the islands in Hawaii. These islands are formed by a hotspot, which is a place where magma wells up from deep below. As the ocean floor moves, it creates a long trail of volcanoes.

Shield volcanoes can become incredibly huge. Mauna Loa in Hawaii is one of the largest active volcanoes on Earth. It is so heavy that it actually pushes down the Earth's crust. From the sea floor to the top, Mauna Loa is about 30,000 feet tall. That is much taller than Mount Everest!

You can even find giant ones in space. Olympus Mons on Mars is a massive shield volcano. It is much larger than any volcano on Earth.

You can see different kinds of lava when these volcanoes erupt. Some lava is smooth and has a ropey texture. This is called pāhoehoe. Other lava is thick, blocky, and moves more slowly. This type is called ʻaʻā. These different flows help build the volcano's shape over many years. Even though they look calm, these volcanoes are powerful forces that change the shape of our planets.

A shield volcano is a massive volcanic structure defined by its low profile and broad shape. This distinct form resembles a warrior's shield lying flat on the ground.

Unlike other volcanic types, shield volcanoes are built by the eruption of highly fluid lava. This lava has low viscosity, which means it is thin and runny. Because it flows so easily, it can travel great distances from the eruption site. Over many repeated eruptions, these thin layers of lava accumulate to create a wide, gently sloping mountain.

The construction of a shield volcano is a steady, long-term process. Most eruptions are described as effusive, meaning they are gentle rather than explosive. These eruptions involve the emission of basaltic lava with low gas content. This lava often flows out of central vents or along decentralized fissure vents. A fissure is a long crack in the ground that can create a "curtain of fire" or a "wall of fire."

As the lava travels, it can move through lava tubes. These are cave-like structures formed when the top layer of lava hardens. The walls of these tubes insulate the molten rock inside, allowing it to travel much further. In fact, about 58% of the lava at Kīlauea moves through these tubes.

Scientists categorize different types of lava flows based on their texture and movement. One common type is pāhoehoe, which is relatively smooth and has a ropey appearance. The other type is ʻaʻā, which is denser and more viscous, meaning it is thicker and moves more slowly. ʻAʻā lava often forms into blocky shapes. These flows move through a specific pressure mechanism. The partially solidified front of the flow steepens because of the weight of the lava behind it. This causes the front to break off and move forward. While pāhoehoe can turn into ʻaʻā if the lava becomes more viscous, the reverse never happens.

While most shield volcanoes are made of basaltic lava, there are rare exceptions. Some are called pyroclastic shields, which are formed by the accumulation of fragmented material from powerful explosive eruptions. Examples include the Billy Mitchell volcano in Papua New Guinea. There are also rarer felsic lava shields formed by unusually fluid felsic magmas. The Ilgachuz Range in British Columbia is an example of a felsic shield. Most mature shields also feature cinder cones on their flanks. These are smaller, secondary volcanic cones formed by the ejection of tephra during activity.

The history of the term "shield volcano" began with the Austrian geologist Eduard Suess. In 1888, he coined the German term "Schildvulkan." By 1910, the term had been translated into English. Much of our modern scientific understanding comes from studying the Hawaiian Islands. These islands are formed by a hotspot, which is a place where magma wells up from deep within the Earth. As the oceanic plate moves over this hotspot, it creates a long trail of volcanoes across the seafloor.

Shield volcanoes can reach staggering dimensions. Mauna Loa in Hawaii is one of the largest active volcanoes on Earth. Its mass is so great that it has caused the Earth's crust to slump downward. When you measure from its base on the sea floor to its summit, Mauna Loa is about 30,000 feet tall. This makes it much taller than Mount Everest.

Even larger structures exist in our solar system. Olympus Mons on Mars is a giant shield volcano that dwarfs any volcanic feature found on Earth.

These volcanoes are found in many different environments across the globe. They often form over hotspots, such as the Galápagos Islands, or over continental rift zones, like those in East Africa. They can also appear in ocean basins or near subduction zones, such as in California and Oregon. Some lava flows from these volcanoes create vast plateaus. In places like Idaho and Washington, these basaltic plateaus can reach thicknesses of over 1,000 feet. Whether in the ocean or on land, shield volcanoes are powerful builders of planetary surfaces.