Small earthquakes and a so-called “inflation” of the mountain, signaling a potential volcanic eruption, have been reported near Iceland’s famous “Blue Lagoon,” local authorities said Monday.

The Icelandic Met Office declared a state of uncertainty over the weekend, following days of several smaller earthquakes and a swelling of the mountain.

Alert levels for aviation were also raised from “green” to “yellow,” defined as when a volcano “is experiencing signs of elevated unrest above known background levels.”

For nearly a week, a series of earthquakes have been shaking the area around Grindavik, not far from the steaming waters of the “Blue Lagoon,” a popular geothermal spa in southwestern Iceland on the Reykjanes Peninsula.

The largest recorded quake had a magnitude of 3.7.

Swarms of earthquakes are not unusual in the area, but the fact that they were occurring alongside an “unusually fast” inflation of Mount Thorbjorn, a few kilometers (miles) from Grindavik, was “a cause for concern and closer monitoring,” according to the Icelandic Met Office.

Read more: AFP