Could an expert in this field explain this video, most notably the last 1-2 minutes that show the map of receding ice, and the years it took for ice to recede.
My wife and I are discussing this and it seems that the brief narration does not NEARLY explain what the map means. What the depth of the ice was in 1900, what the depth was in 1990, what it is now. It APPEARS that the ice is receding out towards the ocean on the right, slowly pulling out from its intrusion into/ onto land mass.
But… someone please explain what this map is really telling us?
I get the part where lower Manhattan has disappeared in a roiling mass of chaos. Got that. Amazing video with perspective. But the map and data shared at end of the video need explanation.
I am no glaciologist, but I think the physics are pretty straightforward. For centuries or more, this fjord has been filled with ice, resting on the seafloor, pressed down by its’ own weight. It has more or less held its’ lines, gradually flowing outwards to the sea (on the left) as chunks have broken off from the edge. Due to rising temperature, however, during the last century the thickness of the edge of the glacier has decreased to the point when the weight cannot longer match the buoyancy - so it takes to float, at which point it breaks up in huge masses. And this seems to have happened increasingly fast - in the last decade, it has receded more than in the previous century.
I think you’re perception of the map is confused. The glacier sits on land and the ocean is to the left. At its edge, it’s an ice shelf with liquid water underneath, but it’s still attached to ice which sits on solid ground (further east). As the glacier calves, the ice breaks off and flows away westward, melting.
Keep in mind that glaciers “flow”. Layers upon layers of ice all exert immense force on the layers below, and the ice deforms plastically outwards. At those pressures it’s a lot like pushing down on a piece of brie cheese and making the sides bulge outwards. Precipitation on the glacier constantly adds more weight, and the ice underneath constantly flows.
In summer, the melting speeds up and in general, more ice melts at the edges than flows from the center, and the glacier “retreats”. This doesn’t mean any piece of ice is actually moving uphill, but rather the edge of the glacier is. In winter, in general, the melting slows. More ice moves in and less melts, so the edge actually does move downhill and the glacier “advances”.
The map in video is showing the multi-year trend of that process. Measurements taken at the height of summer (or possibly the height of winter) show the glacier’s position of maximum retreat. Each year, that maximum is further and further uphill; the glacier is melting faster than precipitation can resupply it.
