Tuesday, 4 July 2017

Dry Valleys and Lake Vanda - wonderful Antarctica

'There is a place on earth that is so unlike anywhere else on earth that it has been used to test equipment intended for use on Mars.'

The Dry Valleys region of Antarctica is one of the world's most extreme deserts, but that's only the start.

A dry valley in the Transantarctic Range.

Dry Valleys, Southern Antarctica.
Coordinates: 77° 28′ S, 162° 31′ E

The Dry Valleys are located on the western coast of the Ross Sea.

The Dry Valleys in southern Victoria Land, 100 km west of McMurdo station, form the largest ice-free area in Antarctica (4800 km2). They are the most extreme cold desert anywhere on earth, where the mean annual temperature is between -14º C and -30º C, most frequently under -20º C, and reaching a record low -68º C.

The Dry Valleys are protected from the ice masses of the Polar Plateau by the Transantarctic Mountains. They force air flowing upwards so they lose their moisture; the valleys then are in a precipitation shadow (where snow and rain don't fall).

Bull Pass, a low passage north of Wright Valley that shows clearly the contrast between "normal" iced Antarctica and the Dry Valleys.

The mountains also prevent the flow of ice down the valleys from the East Antarctic Ice Sheet and finally, strong katabatic winds of up to 320 km/h blow down from the interior along with the low humidity causing the ice from the glaciers that do discharge into the valleys to evaporate.

Wright Valley, the largest of the main three valleys; at far, lake Vanda.

There are three large valleys, Taylor Valley, Wright Valley and Victoria Valley (the great Queen is everywhere!). Taylor Valley was first discovered during Scott's Discovery Expedition (named after the ship) in 1901-1904. It wasn't until the 1950's that further valleys and their extent were discovered from aerial photography.

Taylor Valley. The montain top glaciers drop down to the valley but they can't feed the bottom with ice or melt water - winds evaporate the tiniest humidity.

It's been 2000 million years at least without rain falling.

Glacier sliding down to Taylor Valley.

Unexpectedly, in all this dryness there are rivers flowing, yes! No lush vegetation though, and no fish, but beauty is there somehow. At least, humans are hundreds of miles away, that's already a bit of paradise... Mostly everywhere Man just ruins Nature.

Maybe the most impressive is Wright Valley, through which flows the river Onyx to feed Lake Vanda. These names even sound like Scy Fy !

River Onyx and Lake Vanda, in Wright Valley.

During austral summer, the lake partially melts. River Onyx (left) flows into Lake Vanda.

Lake Vanda is the largest of several lakes, at 5.6 km x 1.5 km at extremes, with a depth of 69 m, it has a smooth ice cover of around 4 m thick, in the summer a moat develops as the shore ice melts. Water comes from summer melting of nearby glaciers, once a balance occurs between water entering the lake and ice sublimation from the surface, leading to a fairly stable situation.

The rocks here are granites and gneisses. Loose gravel covers the ground.

Lake Vanda is a hypersaline lake with a salinity more than ten times that of the Dead Sea. Lake Vanda is also meromictic, which means that the deeper waters of the lake don't mix with the shallower waters. There are three distinct layers of water ranging in temperature from 23 °C on the bottom to the middle layer of 7 °C and the upper layer ranges from 4–6 °C .

As there is little or no snowfall in the Dry Valleys the ice on the surface of the lakes is exposed and can be quite beautiful, very hard and clear blue, often with inclusions of small air bubbles, radiating and crossed crack lines.

The lake is always covered by a thick iced transparent layer, some 3 to 4 m deep, except in December when austral summer causes some melting in the lake borders.

Some wind blown sand dust remained captured under ice surface.

Cracks, melt lines and bubbles.

Onyx River is the longest in Antarctica - 32 km ; strictly speaking it isn't a river but a seasonal meltwater stream fed by glaciers.

The Onyx River is a meltwater stream which flows westward through the Wright Valley from Wright Glacier, during the few months of the Antarctic summer. Despite being only 32 kilometres in length it is the longest in Antarctica.

Onyx River, Antarctica Dry Valleys
Coordinates: 77° 26′ S, 162° 45′ E

Onyx stream is formed in Summer from melting Wright Glacier and flows inland along the Wright Valley for 28 kilometers until it reaches Lake Vanda. Strangely, it flows inland, away from the sea, its water never reaching the ocean.

The Onyx typically flows for 6-8 weeks in, in some years it may never actually reach Lake Vanda while in others it may flood causing significant erosion to the valley floor.

The stream flow is quite variable - some years it doesn't even flow at all; some other years, overflow causes large floods. As the river flows it supports some algal (cyanobacteria) growth particularly in the wider and shallower areas.

The New Zealander Vanda Station, at the mouth of the river, was removed in 1995 as lake levels rose, and replaced by a shelter - Lake Vanda Hut - that is temporarily staffed in summer by 2-8 researchers (meteorology, sismology, hidrology...).

The New Zealander hut by the lake, bottom centre.

What a wondrous place! I could sit here and rest to die when time comes...