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From an observational stand point we're at a sweet spot

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where we can see many different aspects of the changing ice cover

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and so that the problems are then

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moving toward understanding what we see changing.

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It is pretty clear that we're gonna understand what the ice is doing.

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I think that observational glaciology in terms of remote sensing

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is a very data rich field now

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compared to 1972 when you had a few images.

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So we are beginning to get a historical record of the speeds of glaciers

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and so we can watch how rapidly that surface is lowering

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as things speed up or where it's thickening

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and where the surface is actually coming up

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or where ice is actually thickening on land.

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With this record we can go in and look at the speeds of ice flow

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over decades and how it's been changing

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The reaction I get from other people that study glaciers

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is that I watch these videos too fast.

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I like to see the fluid nature of the ice.

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It lets you see the ice on the land

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as sort of this very active participant in what's going on.

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One of the places that I like to look at in this particular video of Hubbard

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is if you look just to the upper-left off the five kilometer scale bar

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you can watch the edge of the glacier just spread across the the river bed

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that's coming out of the glacier that's adjacent to it.

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And it just moves, it moves trees,

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it moves all sorts of material every single year, just advancing.

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So this video that shows the Walsh glacier on the top

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and the Logan glacier on the bottom,

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these are huge glaciers. They're the order of four kilometers wide or so.

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What we see as we loop through it is that the flow in both of these

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sits there for years and then it will undergo

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a pulse of faster motion and then sit there again.

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What strikes me about this image of the Malaspina

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is that you can really see its nature,

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which is that it's a large puddle of ice.

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You've got huge glaciers that are flowing down

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out of a really high mountain range.

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And these big glaciers reach the coastal plain

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and the ice just spreads out in this big puddle,

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like you've taken a bottle of syrup,

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and just dumped it in the middle of a plate.

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The Malaspina is sort of that big pile of syrup.

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The other thing that you see is that

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the ice coming in will head either to the left or the right of center,

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for a while, and it will string out those moraines

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so that they get bent into these loop shapes.

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And you know it wasn’t until I saw this video

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that I felt like I had a good understanding of just

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what was producing these amazing loops in the moraines.

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In compiling this Landsat record,

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from Landsat 1 in 1972 up through today,

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I've gone through year by year and I've tried

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to pick out the latest melt season image I can.

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So the white snow of winter is gone and you can see the detail

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and the flow stripes and the crevasses in the ice.

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And build annual mosaics that give us an

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image of all of the ice in Alaska and the Yukon.

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And when those are all lined up - all 48 of them are lined up

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and played as a movie - we can see the behavior

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of the ice over nearly half a century.

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Having such a long record allows us to discern long-term trends

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and separate them from the kind of behavior you might get

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with a couple warm or a couple of cold years.

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To have a persistent observational capability

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that's been in place ever since the first Landsat was launched,

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it really gives us a much better view of this

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really rapidly changing part of our planet.

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