First you hear a savage cracking sound, next the rolling crash of thunder.
Then as the icebergs rip away from the margin of the ice-sheet they plunge into the grey waters of the Atlantic with a roar that echoes around the mountains.
Nothing prepares you for the sheer scale and drama of events in this forbidding terrain and all the signs are that the changes at work here are gathering pace.
In some places, the ice is melting one metre a month
The only way to reach the ice-sheet is by helicopter - a spectacular flight through remote fjords and the jagged blue-white rubble of the ice.
We travelled with Danish scientist Carl Boggild of GEUS, the Geological Survey of Denmark and Greenland.
For the past few years he has been managing a network of 10 automatic monitoring stations and his first results are alarming - the edges of the ice-sheet are melting up to 10 times more rapidly than earlier research had indicated.
Cracks and crevasses
In 2001 NASA scientists published a major study based on observations by satellite and aircraft.
It concluded that the margins of the Greenland ice-sheet were dropping in height at a rate of roughly one metre a year.
Scientists have traced the retreat of the Sermilik glacier
Now, amid some of the most hostile conditions anywhere on the planet, Carl Boggild and his team have recorded falls as dramatic as 10 metres a year - in places the ice is dropping at a rate of one metre a month.
The glacier we visited - the Sermilik glacier in southern Greenland - is so volatile that one automatic monitoring station was lost into a yawning crevasse.
Between a maintenance visit in May and our visit this month, new cracks had opened up in the icy surface and we had to help shift one of the devices to a safer position.
Engravings from the late 19th Century show how the glacier once reached far into the ocean and satellite pictures highlight how the retreat has accelerated - the glacier dropping an astounding 150 metres in the last 15 years.
The latest data shows the melting picking up even more speed.
A vicious wind whipping across 2,000 kilometres of solid ice - the length of the Greenland ice-sheet - chilled us as we filmed.
But the feeling of cold was ironic - it is the rise in air temperatures recorded here that is at least partly responsible for the sudden acceleration of the melting.
A hundred years ago the glacier reached into the sea
Dr Boggild and his colleagues, studying the physics of how the air and ice relate, conclude that as much as 55% of the melting is attributable to warming in the air.
He is cautious to avoid blaming climate change too readily: "Maybe if we look back after 50 years and see how temperatures have risen, then we can call it climate change."
Sea level rise
Dr Boggild is all too aware of how easily he could be accused of jumping onto a climate change bandwagon.
But he is adamant that the results he has gathered so far are reliable.
"We can say for certain that the rate of melting has increased and we can say for certain that the height of the ice-sheet is falling, even allowing for increased ice-flow.
Potatoes are growing for the first time in centuries
"There is no doubt that something very major is happening here."
As we speak, he checks the instruments on the automatic station. A large range of data is collected and transmitted via satellite to Copenhagen every six hours.
For the first time, scientists should have a long-term, on-the-ground view of the changes taking place here.
Just before we leave, there is another roar as more icebergs crash into the ocean
Many more icebergs falling into the sea will cause two things to happen - the sea-level will rise and the injection of freshwater could disrupt the ocean currents, including the Gulf Stream.
What happens in this remote barren land has the potential to affect us all.