Permafrost

Some ground stays frozen for a long time.

This frozen ground is called permafrost. It stays cold for two years or more. Some of it has been frozen for a very long time.

This ground is under the top layer of soil. The top layer freezes and thaws with the seasons. Permafrost is found in many cold lands. It is in places like Alaska and Canada. It is also in high mountains.

When this ground gets warm, it can melt. This can make the ground move or sink.

Permafrost is ground that stays frozen for two years or more.

It can be soil or sediment under water. Some permafrost has been frozen for 700,000 years! It is often found under an active layer. This top layer of soil freezes and thaws each season.

Most permafrost is in the Northern Hemisphere. It covers large parts of Alaska, Canada, Greenland, and Siberia. It also exists in high mountains like the Andes.

Permafrost holds much dead plant matter. Because it is frozen, this matter does not rot. As the world warms, the ground thaws. This lets out gases like carbon dioxide or methane. These are greenhouse gases. They can make the climate change even more. Thawing also makes the ground unstable. It can cause the ground to shift or sink. This can hurt buildings and roads.

Thawing can also leak old waste or mercury into nature. Scientists also watch for tiny germs that might wake up. However, the risk from these germs is thought to be low.

Permafrost is ground that stays frozen for at least two years.

It can be made of soil, rock, or sediment under the water. Some of this frozen ground is very old. The oldest parts have stayed frozen for about 700,000 years!

This ground is very important for our planet. It acts like a giant freezer for the Earth. It keeps many things locked away deep inside the soil. This helps keep the world's climate in balance.

Most permafrost sits under a top layer of soil. This top layer is called the active layer.

The active layer freezes and thaws every single year. During summer, the sun warms this top part. This allows plant roots to grow in the soil. Below this, the permafrost stays cold and solid. The line where the active layer meets the permafrost is the permafrost table. This layer stays frozen because the air stays cold for a long time.

Scientists have studied these frozen lands for many years. People began looking closely at mountain permafrost in the 1970s.

This was a hard job because mountains are difficult to reach. Even so, they found permafrost in many new places. In 2009, they found it on Mount Kilimanjaro in Africa. This mountain is very high and near the equator. It shows that cold ground can exist in many different parts of the world.

Permafrost covers a huge amount of our planet. It covers about 15% of the Northern Hemisphere.

You can find it in Alaska, Canada, Greenland, and Siberia. It also exists in the Tibetan Plateau. In the Southern Hemisphere, it is mostly on mountain slopes. You can find it in the Andes or the Southern Alps of New Zealand. Some permafrost is even under the sea on continental shelves. This happened when sea levels were lower during the last Ice Age.

Thawing permafrost can change how the world works.

It holds much dead plant matter called biomass. When the ground thaws, this matter starts to rot. This releases gases like carbon dioxide or methane. These gases can make the Earth even warmer. Thawing also makes the ground soft and unstable. This can cause buildings to sink or roads to break. Nearly 70% of buildings on permafrost could be at risk by 2050.

Permafrost is defined as soil, rock, or underwater sediment that remains continuously frozen for at least two years.

This frozen ground serves as a massive storage system for the planet. Some of the oldest permafrost has stayed frozen for approximately 700,000 years. The vertical depth of permafrost varies greatly depending on the location. Some areas have a depth of less than one meter. Other regions contain permafrost that is deeper than 1,500 meters.

It is a critical component of the Earth's cryosphere and climate systems.

On land, permafrost typically exists beneath a seasonal layer called the active layer.

The active layer is the top portion of soil that freezes and thaws every year. This seasonal cycle allows plant roots to take hold during the warmer months. The boundary between this seasonal layer and the permanently frozen ground is known as the permafrost table. Below this table, the ground stays at or below 0°C. In the deepest sections, the temperature profile eventually meets geothermal heat from the Earth's crust. This heat eventually warms the ground back above the freezing point.

Scientists classify permafrost into three main types based on how much land it covers. The first type is continuous permafrost, which covers 90% to 100% of a specific area. This is often found in the coldest Arctic regions. The second type is discontinuous permafrost, which covers between 50% and 90% of the landscape. This is often called the extensive discontinuous permafrost zone (DPZ). The third type is sporadic permafrost, which covers less than 50% of the area. This is often called the sporadic permafrost zone (SPZ).

These zones depend heavily on the mean annual air temperature.

Permafrost is found across many different parts of the globe. In the Northern Hemisphere, it covers about 15% of the land area. This includes massive regions in Alaska, Canada, Greenland, and Siberia. It also exists on the Tibetan Plateau. In the Southern Hemisphere, permafrost is less common and mostly found on mountain slopes. Examples include the Andes in Patagonia and the Southern Alps of New Zealand. Some permafrost is also located in Antarctica.

Additionally, subsea permafrost exists beneath the seabed on continental shelves. This was formed when sea levels were lower during the last Ice Age.

Research into permafrost has evolved significantly over time. Systematic studies of alpine permafrost did not begin until the 1970s. High mountain regions are particularly difficult for scientists to study. In 2009, researchers discovered permafrost on Mount Kilimanjaro in Africa. This was a surprising find because the mountain is near the equator. By 2014, regional estimates suggested that global alpine permafrost covered about 680,000 square kilometers. These discoveries help scientists map how much frozen water is stored in mountains.

Thawing permafrost creates a significant climate change feedback loop.

The ground contains large amounts of dead biomass that has accumulated over millennia. Because the ground was frozen, this organic matter could not fully decompose. As global warming heats the ecosystem, this soil thaws. This allows decomposition to start again. This process releases greenhouse gases like carbon dioxide or methane. These emissions can impact global carbon budgets. Annual emissions are estimated to be comparable to those from large countries like Russia or the United States.

Beyond climate impacts, thawing permafrost poses many physical and environmental risks. When ice-rich ground thaws, it can become saturated with water. This causes the ground to shift or collapse entirely. This instability threatens human infrastructure. It is estimated that nearly 70% of buildings on permafrost are at risk by 2050.

There are also concerns about pollution. Between 13,000 and 20,000 sites containing toxic waste are located in permafrost. Thawing could also release natural mercury deposits. While some worry about ancient pathogens, scientific reviews currently describe that risk as generally low.