Blades of ice rising from the ground up to several meters high: penitentes are a common sight in the Andes. How are these peculiar ice spires, named after their resemblance to religious orders doing penance, formed?
A field of dazzling white jagged ice spires towering as high as five meters tall: stunning to look at, but not so fun to cross, as the famous naturalist Charles Darwin found when he had to squeeze his way through them on his travels in 1835.
Darwin was on his way from Santiago de Chile to the Argentinian city of Mendoza and came across the snowfield covered with penitentes near the Piuquenes Pass.
The first written record of penitentes is thought to be from Darwin, who wrote in 1839: "Frozen masses, during the process of thawing, had in some parts been converted into pinnacles or columns, which, as they were high and close together, made it difficult for the cargo mules to pass.
"On one of these columns of ice, a frozen horse was sticking as on a pedestal, but with its hind legs straight up in the air. The animal, I suppose, must have fallen with its head downward into a hole, when the snow was continuous, and afterwards the surrounding parts must have been removed by the thaw."
He reported the mistaken belief held among the locals there that these penitentes were formed by the strong winds of the Andes. We now know that wind doesn’t play a role in creating penitentes, named after their resemblance to the white pointed hoods of religious orders performing penance processions during Spanish Holy Week.
It is how they melt that give these snow and ice formations, found on glaciated and snow-covered very high-altitude areas where the air is dry, their spectacular shapes.
Found in places such as the Andes mountains above 4,000 meters (13,120 feet) high, they take the form of tall thin blades of hardened ice or snow clustered closely together with their spikes pointing towards the general direction of the sun. They are created when the sun's rays turn snow directly into water vapor without melting it first - a process known as sublimation.
A smooth snow surface, initially smooth, first develops depressions as some regions randomly sublimate more quickly than others.
The curved surfaces then focus the sunlight and acceleratae sublimation in the depressions. This leaves behind the towering spikes. They can range in size from a few centimeters to two meters tall, but some as high as five meters (16 feet) have also been found.
Scientists have argued that the presence of carbon or any other impurities lead to some absorption of sunlight, leading to penitentes, claiming that the glaciers could therefore be saved from the onslaught of global warming.
But there are are counter arguments to this claim, saying that if the penitentes absorb more sunlight due to the presence of carbon, they may also result in the destruction of the icebergs. Scientists are researching into the effects of global warming on how penitentes are formed.