Geothermal activity

Geothermal activity is a cool natural process where heat from deep inside the Earth moves up to the surface. This happens because there is extra heat stored underground, often from rocks formed from cooled-down magma, called igneous intrusions.

A fumarole in the Solfatara crater, the orange and yellow colouration is from minerals that are deposited by the superheated fumes as they cool to ambient temperature.

This activity can create many interesting sights and changes in the land. You might see places where the ground is warmer than usual, or find areas with hot water flowing out, known as hydrothermal activity. Another common sign of geothermal activity is fumaroles. These are openings in the Earth that release hot gases from volcanoes.

Studying geothermal activity helps scientists learn more about Earth's inner workings and shows us ways to use this heat as a clean energy source for the future.

Background physics

Main article: Earth's internal heat budget

Mud pots in the Sol de Mañana Hydrothermal field, Bolivia. The yellow coloring in the soil derives from deposits of sulfur.

Geothermal activity often happens near volcanoes. The heat comes from melted rock deep underground. Heat can also come from fires, radioactive materials, or natural processes like the movement of substances, friction from tides, or changes in rocks. This heat reaches the surface slowly through the ground or by moving with water or gases.

Types of geothermal activity

Fumaroles, or volcanic vents, are openings in the ground where hot gases escape into the air. They are often found above a magma chamber, which sends up hot gases through spaces in the rock. When these spaces reach the surface, they create fumaroles. Areas with many of these vents are called fumarole fields. These vents can leave behind certain minerals when the gases cool in the air.

Ice cauldrons happen when an ice cap is warmed by geothermal heat, either from volcanoes or hot areas underground. These cauldrons can look different, from small dents in the ice to deep holes with steep sides.

Main article: Ice cauldrons

Hydrothermal activity

Geothermal heat and groundwater can interact in several ways.

Geysers

Geysir, a geyser in Iceland, after which the phenomenon is named.

Geysers are the most well known hydrothermal feature. They occur when groundwater deep underground gets very hot under a layer of colder water on top. When this hot water reaches the surface, it turns to steam quickly. This causes the pressure below to drop suddenly, making more water turn to steam all at once.

There are two main types of geysers. Fountain geysers burst out violently from a pool, and cone geysers spray out steady jets for minutes from a cone-shaped pile of minerals built up around the vent.

Two Hot springs in Waiotapu, New Zealand, with Artist's Palette in the foreground, and Champagne Pool directly behind it in the background.

Hot springs and mud pots

In other places, the hot water collects in pools, creating hot springs. Where there is very little groundwater, hot water rising up mixes with tiny living things and forms mud pots. The way these mud pots behave can change with the seasons depending on how much rain there is and how high the water table is.

Hydrothermal explosions

Hydrothermal explosions happen when very hot water deep underground cannot reach the surface. The pressure builds up until it reaches a breaking point, causing an explosion. This ejects the hot water and rocks from underground.