Origins ANTARCTICA, Scientific Journeys from McMurdo to the Pole
Ideas Tools Place Live Field Notes
Blue light inside a fumarole on Mt. Erebus.
Click to enlarge.

Antarctic Light

Sunlight and ice combine to create natural art.
by Paul Doherty

December 13, 2001

The light in Antarctica presents me with new colors and images every day.

Observation 1: Noel and I descended into one of the ice towers made by fumaroles on Mt. Erebus. Fumaroles are vents from which volcanic gas escapes into the atmosphere. Ice towers are formed when the hot gas condenses into ice deposits. Light filtering down through the ice at the entrance was white. As we moved deeper under the ice the light became deep blue because the water molecules locked together in the ice absorbed the red from the sunlight. Until, at the very deepest levels, the light became a stunning violet.

Observation 2: The smoke plumes from Erebus were bluish in color. As the plumes moved toward us their shadows on the snow were yellow and yellowish-brown. Yellow and blue are complementary colors, they add together to make white. When the clouds scatter the blue light out of the white sunlight, only yellow light continues on to strike the snow.

Observation 3: At Lower Erebus hut, the plume of Erebus passed between me and the sun. The sun was immediately surrounded by three reddish rings of corona about 12 degrees in total diameter. The appearance of the circular coronal rings told me that the cloud was made of supercooled water droplets, not ice crystals. It was fun to see the sun as the bull;s eye in a three-ring target.

A Fata Morgana creates illusory cliffs at the base
of Mt. Discovery.

Observation 4: Outside the window of our office in Crary Lab we look across McMurdo Sound to Mount Discovery. One calm morning it looked like someone had lifted up the entire mountain and that the bottom had stretched upward like taffy. There seemed to be a new set of cliffs ringing the bottom of the mountain. It was a Fata Morgana, an inferior mirage—a mirage that appears below an object—and light from the mountain bent as it passed through different temperature layers of air above the ice. Fata Morganas are named after Morgan le Fay, sister to King Arthur, who was supposed to be able to change her shape.

field notes
Origins Exploratorium ANTARCTICA


© Exploratorium