Giant sinkholes discovered on Arctic seafloor

Scientists mapping the seafloor in the Arctic have made a startling discovery. Giant sinkholes.

Some of the sinkholes are larger than a city block.

The sinkholes are developing due to melting permafrost that has been submerged underneath the seabed.

These changes have occurred in less than a decade.

What is permafrost?

Permafrost is ground that continuously remains below freezing and can be located on land or under the ocean.