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[music throughout]

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My name is Sean Healey,

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I study forest dynamics.

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I study changes in carbon,

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changes in forest structure when they are disturbed,

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that is burned or cut down.

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I also study recovery,

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which is what we see a lot of following the eruption of Mount St. Helens.

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I visited it for the first time 20 years after, it was like a moonscape.

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A lot of it was still like a moonscape: 

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you know, pieces of pumice on the ground, no vegetation.

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It has been a place of extraordinary change over the last forty years.

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From really beautiful old growth forest to a moonscape.

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And then back again to a lot of unbroken

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sort-of twenty year-old forests, pretty high canopy cover.

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Uh, a lot of trees there now.

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From the fringes of the blast zone,

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you definitely see patterns of revegetation.

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They start slowly, with a little bit of greening,

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but by the time you get to the end of the time series,

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it looks pretty dark green. And you see the same thing on the ground.

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You see you know maybe not a forty year old forest,

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but something that looks thirty years old.

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And in this part of the country, trees are pretty tall after thirty years.

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What we’re looking at is Mount St. Helens

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in southwestern Washington, in 1973.

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Snow cover is what you see as white there,

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right in the middle of the mountain.

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It’s surrounded by some dark, deep reddish forests,

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which is basically how this MSS imagery sees older growth forests.

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To the east of it we se a lot of very active timber harvests.

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All of those patches of blue are recent clear cuts.

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Just to the north of the mountain, there,

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you see a very large clear cut.

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That one happens to be about two square miles,

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which is really really large by today’s standards. 

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And then Spirit Lake, just to the northeast of the volcano.

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You will see that the shape of that lake will change,

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radically, after the volcano erupts.

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Well, in this image, I mean, if you remember that large clear cut

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that I pointed out you can see that it is starting to go from that bluish cast

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to having more red, which indicates, you know, recovery following harvest.

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And six years has passed, so you would definitely expect that

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in a very productive forest like this one.

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And it has been joined by a lot more clear cuts in that area, too.

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I have looked at a lot of Landsat scenes.

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This is the biggest change from one image to another that I can think of.

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Forests and everything else, many miles to the north, were just incinerated. 

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The blast and the heat and the ash really levelled a lot. 

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It looks from this image like Spirit Lake, just to the northeast of the volcano

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is not there, but it is there, it’s covered in logs.

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And most of the water in that lake got splashed up six hundred feet or more,

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and sort of dragged all of the trees that were on that wall down.

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Over the forty years since the eruption,

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you know, we do see that recovery happens first

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in the places that didn’t have that huge blast of heat

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and were not covered with many, many meters of ash or mud.

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In ’84, the first Thematic Mapper Landsat was launched.

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So that really changes our ability to display this kind of image

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in something closer to true color so it’s much more intuitive: 

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green means green.

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So from this point forward you can sort of visualize

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the encroaching greenness

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which indicates the re-vegetating and re-foresting areas after the eruption.

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Well, I’ll also point out some of the remaining old growth forest

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that you can see in that very dark patch.

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In the MSS imagery, that was dark red.

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It’s just much more intuitive to spot that kind of dark green

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when we can display it in true color.

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You can see in the early ‘90s clear cuts starting to pop up.

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So basically it looks like it is going from green

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to some kind of brownish color.

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Even as the outer edge of these clearcuts are growing and filling in,

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the inner edges are greening up and turning green.

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And by the end of the time series they look pretty green,

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even though we just saw them get cut thirty years before that.

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So we have basically made a model

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that uses the imagery to predict what percent cover there is.

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Basically, how thick is the tree canopy here.

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And through the time series, you can see much of the blast zone

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going from red, which is zero trees,

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to pretty green, which is, you know, pretty solid tree cover.

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And that is really solid documentation of the recovery of the forest in this area.

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You can also see its neighboring places go from green to red

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in the opposite direction. Obviously there are harvests happening

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and those are taking away forest canopy

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at the same time that recovery is adding forest canopy

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in the place that was affected by the eruption.

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The really unique part about the Landsat record

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is the fact that it goes back to the ‘70s.

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I can’t imagine what it would be like to describe

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what this volcano did without having a time series of Landsat.

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We’ve got eight years before the eruption and forty years after the eruption.

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There is no other asset in the sky that can show us what Landsat does,

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in terms of the effect of the eruption

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and also the effect of the recovery following the eruption.

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Uh, it’s just amazingly lucky that Landsat was up there

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in its spot in the sky to watch this whole thing unfold.

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Let’s hear it for Landsat. 

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