Alarming evidence of melted ice cascading down icy cliffs in Antarctica has raised new fears among scientists.

Scientists once thought the presence of meltwater streams during Antarctica's short summer was rare and restricted to small areas.

But new research has revealed how streams and lakes made from melted ice crisscross much of the icy continent's surface - and they may have been for decades.

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Massive summer melting on East Antarctica's Amery Ice Shelf, seen from NASA's Landsat 4 satellite. The image shows about 520 square miles

In the first continent-wide survey, scientists have found extensive evidence of meltwater flowing over parts of Antarctica's ice during its brief summer.

Researchers already knew such features existed, but assumed they were confined mainly to Antarctica's fastest-warming, most northerly reaches.

Many of the newly mapped drainages are not new, but the fact they exist at all is significant, researchers said.

They added that the streams appear to worsen with small upswings in temperature, so global warming could quickly magnify their influence on sea level.

'This is not in the future, this is widespread now, and has been for decades,' said lead researcher Jonathan Kingslake, a glaciologist at Columbia University's Lamont-Doherty Earth Observatory.

'I think most polar scientists have considered water moving across the surface of Antarctica to be extremely rare.

Scientists have discovered that seasonally flowing streams fringe much of Antarctica's ice. Each red 'X' represents a separate drainage. Up to now, such features were thought to exist mainly on the far northerly Antarctic Peninsula (upper left). Their widespread presence signals that the ice may be more vulnerable to melting than previously thought

'But we found a lot of it, over very large areas.'

Explorers and scientists have documented a few Antarctic melt streams starting in the early 20th century, but no one knew how extensive they were.

The researchers found out by systematically cataloguing images of surface water in photos taken by military aircraft from 1947 onward and satellite imagery from 1973 to present day.

They found nearly 700 seasonal systems of interconnected ponds, channels and braided streams fringing the continent on all sides.

Some run as far as 75 miles (121km), with ponds up to several miles wide.

They start as close as 375 miles (604km) from the South Pole, and at 4,300 feet (1,311m) above sea level, where liquid water was generally thought to be rare to impossible.

Seen from an aircraft, a 400-foot-wide waterfall drains off the Nansen Ice Shelf into the ocean

The data is too sparse in many locations for the researchers to tell whether the extent or number of drainages have increased over the seven decades covered by the study.

'We have no reason to think they have,' said Dr Kingslake.

'But without further work, we can't tell.

'Now, looking forward, it will be really important to work out how these systems will change in response to warming, and how this will affect the ice sheets.'