Hverarond is a geothermal field in Krafla caldera area near Mvatmn Lake which is full of mudpots, steam vents, sulphur deposits, boiling springs and fumaroles.

A mudpot — or mud pool — is a sort of acidic hot spring, or fumarole, with limited water. It usually takes the form of a pool of bubbling mud. The acid and microorganisms decompose surrounding rock into clay and mud.

https://en.wikipedia.org/wiki/Mudpot