Antarcticas volcanic ice caves

A topsy-turvy world

Mount Erebus is the most southerly active volcano on the planet. It began to form about 1.3 million years ago and today stands 3,794m above sea level. Its slopes are covered with snow and ice, glaciers, crevasses and the occasional lava flow, but steam usually rises from its summit, betraying the intense heat within. If Erebus were a dessert, it would be a reverse Baked Alaska – frozen on the outside and hot in the middle. (Carsten Peter/National Geographic Stock)

Below the surface

The volcano, including the frequency of its eruptions, the types of gases it gives off, and the age of its rocks, is well studied. But the thousands of microscopic organisms that live in the hot soils inside the caves near Erebus’ summit make up one of the planet’s least known ecosystems. It could also be one of the largest – some estimates suggest that one-third of all bacteria on the planet might live there – and weirdest. These microbes do not survive by drawing energy from the sun. Instead, they get energy from other sources, such as iron or hydrogen. (Carsten Peter/National Geographic Stock)

Drilling deep

Until recently the study of the microbes was problematic: if you could not grow it in the laboratory, how could you describe it, let alone study it? In the past decade or so, though, genetic techniques have been developed that allow whole communities of microbes to be characterised by their DNA alone, giving scientists a far more complete picture. A team of eight researchers explored the caves in 2012 using a drill to extract a sample of snow and ice accumulated over many years. The hope is that such samples will contain microbes from inside the volcano, giving a window into microbial life. (Carsten Peter/National Geographic Stock)

True blue domes

Here, microbiologist Craig Cary peers underneath the blue dome of an ice cave, where he will take a soil sample to check for microbes. Although the volcanic soils themselves are hot – they can reach temperatures of 65C – the air just above is not. Move a couple of metres away from the hot spot, and the soil temperature drops sharply. These caves lie close to the surface, with only thin ice separating them from the outside world. Anyone walking outside the cave must take care or risk falling through. (Carsten Peter/National Geographic Stock)

Clusters of crystals

Inside the ice caves, frost crystals form from the volcano’s warm, wet air. Each crystal grows in a different shape depending on how the air currents flow. Here, a team member investigates the passages of Hut Cave, working to find the origin of the microbes that inhabit the caves. (Carsten Peter/National Geographic Stock)