A phonolite furnace in the ice
Mount Erebus, the world's southernmost active volcano, rises 3,794 meters (12,448 feet) above the frozen landscape of Ross Island. At its summit is a persistent, convecting lava lake, a feature found at only a handful of other volcanoes on the planet. This lake of molten rock has been continuously active since at least 1972. The magma is a rare type known as anorthoclase-porphyritic tephritic phonolite. This alkalic lava is low in silica and high in sodium and potassium.
The temperature of the lake's surface hovers between 900 and 1,100 degrees Celsius (1,652 to 2,066°F). Within the main summit crater, which measures 500 by 600 meters across, lies a deeper, 100-meter-deep inner crater that contains the lava lake itself. The volcano's activity is characterized by mild but frequent Strombolian eruptions. These eruptions, which can occur multiple times a day, are caused by large gas bubbles rising through the magma and bursting at the surface. These bursts hurl bombs of lava, sometimes several meters in length, onto the crater rim and surrounding slopes. During a period of increased activity in 1984, some bombs were ejected more than a kilometer from the crater.
Crystals and caves
One of the most unusual products of Erebus's eruptions are large, well-formed crystals of anorthoclase feldspar, sometimes called "Erebus crystals". These crystals grow within the phonolite magma before being ejected, encased in glassy volcanic bombs. The glass weathers away quickly in the harsh environment, leaving a lag of near-perfect crystals, some reaching up to 10 centimeters in length, scattered across the volcano's upper slopes. Their presence provides volcanologists with direct samples of the minerals forming deep within the magmatic system.
The constant heat from the volcano interacts with the overlying snow and ice to create a remarkable network of ice caves and fumaroles. Steam from volcanic vents melts passages through the ice, creating caverns where temperatures can be as warm as 25°C (77°F). In this unlikely, geothermally heated environment, scientists have discovered unique microbial ecosystems. DNA analysis of soil from these caves revealed traces of algae, mosses, and even small invertebrates, suggesting a hidden ecosystem that survives in the dark, nourished by chemical reactions with volcanic gases rather than sunlight.