Graenavatn

Graenavatn fills a maar - a crater blown out by a steam explosion rather than built up by lava - roughly 300 metres across and about 45 metres deep, which makes it deep for its width. The colour that gives it its name comes from a combination of dissolved minerals from the surrounding geothermal ground and algae in the water, and it shifts with light and season rather than staying a fixed shade. Two smaller craters, Gestsstadavatn and Augun, sit alongside on the same fissure. The whole Krysuvik area is thermally active, and the steam of Seltun rises a few minutes further along the road.

Highlights

• A maar crater - blown out by steam, not built by lava.
• Green water about 45 metres deep - minerals and algae rather than one fixed colour.
• Craters on one fissure - Gestsstadavatn and Augun alongside.
• Active ground all around - Krysuvik's geothermal field.

When to go

May to October; road 42 can close in winter. Half an hour.

What to expect

This is a viewpoint stop of ten to twenty minutes, not a walk. The green is subtle in flat light and photographs stronger than it looks. There is no path to the water and the rim is loose. No facilities.

Nearby

Seltun is minutes north; Kleifarvatn lies just beyond it.

Key facts