Glacial flooding has begun from the Eystri Skaftárketill caldera in the Vatnajökull glacier, and is expected to reach populated areas in the region by Thursday.

The Icelandic Met Office has been keeping tabs on the caldera, RÚV reports, and have noticed that the ice in the caldera has been sinking since last Sunday. This particular caldera has not flooded out for five years.

Snorri Zóphóníasson of the Icelandic Met Office advises the general public to avoid the area. Glacial floods can be fast and unpredictable, and it is wise to keep one’s distance.

Glacial floods can be caused by any number of factors – rising lava, eruptions, steam vents or newly opened hot springs can all cause glacial ice to quickly melt, accumulate under the glacier, and then release. The effects can range from minor flooding to powerful destructive forces.