Volcanism

Heat deep inside a planet can melt rock.

This hot, melted rock is called magma. It is lighter than the solid rock around it. Because it is light, the magma rises up.

It can break through the surface. When it comes out, we call it lava.

Some volcanoes erupt mud instead of lava. This happens when gas and liquid push mud up. It is amazing how the ground can change!

Volcanism is when hot stuff erupts from a planet or moon.

This can be solids, liquids, or gases. It happens because of heat inside the body. This heat comes from many places. One way is from radioactive decay. This is when tiny parts of atoms break apart. Another way is tidal heating. This happens when gravity pulls on a moon. This pull changes the moon's shape. This change makes heat.

This heat melts rock or turns it into gas. The melted material is called magma. Magma is less dense than the rock around it. This means it is lighter. Because it is light, it rises to the surface. When it breaks through, we call it lava.

Some places have different kinds of eruptions. On icy moons, water can erupt. This is called cryovolcanism. Instead of hot rock, it uses icy liquids. Mud volcanoes also exist. These happen when gas and liquid push mud up.

They can erupt quietly or with gas.

Volcanism is a powerful way that planets and moons change. It happens when solids, liquids, or gases erupt from inside a body to its surface.

This activity is caused by a heat source deep inside the body. This heat can come from many different places. It might come from the decay of radioactive elements. It can also come from tidal heating, which is caused by gravity.

When this heat builds up, it melts solid material or turns it into gas. This creates the movement we see during an eruption.

There are several ways this melting happens step by step. One way is called decompression melting. This occurs when solid material rises from deep inside a planet. As the material moves upward, the pressure on it drops. This lower pressure allows the rock to melt even if the temperature stays the same. Another way is flux melting. This happens when things like water or carbon dioxide are added to the rock. These substances lower the melting point of the material. This makes the rock turn into liquid more easily.

Scientists have studied many different types of heat and movement. On Earth, we see silicate volcanism where hot rock erupts.

This lava can be thick or fluid. Some lava forms pillow shapes when it hits water. On moons like Jupiter's Io, tidal heating is the main power source. This happens because the gravity of Jupiter pulls on the moon. This constant pulling changes the moon's shape and creates heat. This process is very different from the heat found on Earth.

Different worlds show us many different kinds of eruptions. On icy moons, we see cryovolcanism.

Instead of hot rock, these volcanoes erupt water-based liquids. These liquids are often denser than the ice around them. To reach the surface, they might use gas bubbles to become lighter. We also see mud volcanoes on Earth.

These erupt when gas and fluids push mud upward through sediment. Some of these volcanoes can even release flammable methane gas.

Understanding volcanism helps us see how the solar system works. It connects the deep inside of a planet to the surface we see. On Earth, we can see different textures in cooled lava. Some lava is called A'a and has a very spiny surface. Other types, like Pahoehoe, are much more common.

Even the way a crack in the crust forms matters. A dike is a vertical crack filled with fluid. As magma rises, it can push the crack upward at the top. This shows how much energy is moving beneath our feet.

Volcanism is the process where solids, liquids, gases, or mixtures of these materials erupt to the surface of an astronomical body. This can occur on planets or moons.

It is a fundamental way that celestial bodies transport energy and material from their interiors to their surfaces. This activity is driven by internal heat sources that mobilize material within a body. Once mobilized, this material can rise through the interior and break through the solid surface. Understanding volcanism helps scientists learn about the internal structures of worlds across our solar system.

For volcanism to occur, the temperature of a body's mantle must rise to about half its melting point. At this stage, the viscosity, or thickness, of the mantle drops significantly. When large-scale melting happens, the viscosity can fall from 10^21 Pascal-seconds to 10^3 Pascal-seconds or even less. This change increases the heat transport rate by a million-fold. The melted material is generally less dense and more mobile than the surrounding solid rock. This difference in density provides the buoyancy needed for the melt to rise toward the surface.

There are several ways to generate the heat required for these eruptions. One source is radiogenic heat, which comes from the radioactive decay of isotopes in minerals. Another source is primordial heat, which is the heat left over from a planet's formation. During formation, impacts from planetesimals provided massive amounts of heat. Larger bodies like Earth retain this heat longer than smaller bodies like the Moon. On moons in the outer solar system, tidal heating is often the primary power source. This happens when the gravitational attraction of a large planet deforms the moon's shape, generating internal heat.

Melting can happen through different physical mechanisms. Decompression melting occurs when solid material rises from deep within a body. As the material moves upward, the pressure decreases. This drop in pressure lowers the melting point, allowing the rock to turn into liquid even if the temperature stays the same. Flux melting is another method where the melting point is lowered by adding volatiles, such as water or carbon dioxide.

On Neptune's moon Triton, or possibly on Mars, cryogeyser activity occurs due to external heat from the Sun rather than internal sources.

Once melted, the material must ascend to the surface. In silicate volcanism, melt often collects in pockets or veins. It can flow through rivulets that join to form larger veins. One way it moves is through dikes, which are vertical, fluid-filled cracks. As magma rises in a dike, its lower density causes pressure to fall more slowly than in the surrounding rock. This allows the magma to push the top of the crack upward.

In cryovolcanism, the process is different because the liquid, or cryomagma, is often denser than the surrounding ice. To reach the surface, the liquid must become buoyant through gas bubbles or high pressure from a thickening ice shell.

Volcanism is categorized by the materials being erupted. Silicate volcanism involves silicate materials and occurs at very high temperatures.

When this magma reaches the surface, it is called lava. Silicate lava can be viscous or fluid. Fluid lavas create different textures, such as pillow lava, which forms when lava contacts water, or A'a lava, which has a spiny surface.

Mud volcanoes are another type, where fluids and gases under pressure bring mud to the surface. These often erupt quietly but can release flammable methane. Sulfur volcanism involves lava with a low melting point of about 120 degrees Celsius.

These processes connect the deep interiors of worlds to their visible surfaces. The study of volcanic features, such as impact basins or tidal plumes, provides clues about a moon's composition. For example, the presence of cryovolcanism on icy moons suggests the existence of liquid reservoirs beneath the ice. By observing how lava flows and how cracks form, scientists can map the thermal history of a planet. This helps us understand how heat moves through different types of planetary bodies.