Giant's kettles of Finland

The giant's churn

A giant's kettle is a round, smooth-walled hollow ground into bedrock. The smallest are the size of a pot, the largest are ten-metre shafts you cannot see the bottom of. The walls are so even that the hollow looks machine-drilled. The name comes from what people thought before geology explained it: a hiisi, or giant, had been churning butter in the rock. In Swedish they are jättegrytor, giant's cauldrons.

How a kettle forms

Kettles are traces of the ice sheet's melting phase. As the continental ice sheet thinned around 11,000–10,000 years ago, meltwater rivers ran across its surface and plunged through crevasses onto the bed beneath, under high pressure. Wherever the water struck the bedrock as a vortex, it began spinning stones at the same spot. The stones ground a hollow into the rock, the hollow strengthened the vortex, and the vortex ground further.

The process took hundreds or thousands of years. The grinding stones – pebbles worn smooth – are sometimes still found at the bottom of a kettle. The kettle outcrop at Askola has twenty kettles side by side, which shows that a large river flowed beneath the ice at this spot for a long time.

Not every "kettle" is the ice age's work. Pirunpesät, "devil's nests" such as the hollow on Isovuori in Jalasjärvi, are weathering pits older than the ice age: the rock weathered chemically in a warm climate millions of years ago, and the ice sheet simply exposed the hollow.

Where the kettles are

Kettles are found across the whole country, but the largest concentrations are in Uusimaa (Askola, Nurmijärvi, Helsinki, Vantaa) and Lapland (Salla, Rovaniemi, Inari). In Pihlajamäki, Helsinki, a cluster of kettles sits between apartment blocks. Aholanvaara in Salla and Jumalanhauta in Pudasjärvi are the best known in the north. At Imatra, the kettles lie in the former channel of the Vuoksi, where the rapids have kept eroding the rock ever since the ice disappeared.

Before you go

• A kettle's rim is smooth rock, often damp. Stay on the marked path and keep children close by; the largest kettles have a railing, the smaller ones do not.
• At Askola, the nature trail is 300 metres and ends at a gate, beyond which the kettle area is fenced. At Aholanvaara and Jumalanhauta you walk a forest path.
• In winter, the kettles lie under snow and cannot be seen. The best time is May to October.
• Do not throw stones into a kettle or descend into one without equipment. Many are protected natural monuments.