Uzon Caldera

Uzon is what is left after a volcano collapsed around forty thousand years ago: a caldera roughly ten by nine kilometres with walls two to eight hundred metres high, and a floor that is still thermally active across a wide area. What is on it is a chemical landscape - hot lakes coloured by dissolved minerals and by the organisms living in them, boiling mud pots, sulphur and arsenic crusts, mineral terraces, and Lake Fumarolnoye which stays open through winter. The thermal fields have been studied heavily because extremophile microorganisms live in them, and mineral formation processes here happen fast enough to observe. Bears use the caldera in numbers, feeding on berries and the salmon in the streams. It lies in the Kronotsky reserve, part of the Volcanoes of Kamchatka UNESCO site, and access is helicopter only, normally on the same day trip as the Valley of Geysers, on boardwalks with rangers.

What you actually see

• The caldera - roughly ten by nine kilometres with walls up to eight hundred metres.
• The thermal fields - coloured hot lakes, mud pots and sulphur crusts on the floor.
• The extremophiles - microorganisms studied in water too hot and acid for anything else.
• The bears - using the caldera in numbers for berries and salmon.

When to go

June to September, when helicopters fly. A day, usually combined with the Valley of Geysers. Weather cancels flights often.

Honest expectations

Helicopter only and expensive; cancellations are frequent and many visitors miss it. Ground time is a couple of hours on boardwalks. Leaving the boardwalk is prohibited - thin crusts over boiling ground have killed people at sites like this. Bears are present and rangers set the rules.

Nearby

The Valley of Geysers is on the same flight; Petropavlovsk is south-west.