WEBVTT FILE

1
00:00:00.000 --> 00:00:02.780
[music throughout]

2
00:00:02.800 --> 00:00:04.460
My name is Sean Healey,

3
00:00:04.480 --> 00:00:06.620
I study forest dynamics.

4
00:00:06.640 --> 00:00:09.390
I study changes in carbon,

5
00:00:09.410 --> 00:00:12.200
changes in forest structure when they are disturbed,

6
00:00:12.220 --> 00:00:14.010
that is burned or cut down.

7
00:00:14.030 --> 00:00:15.090
I also study recovery,

8
00:00:15.110 --> 00:00:21.570
which is what we see a lot of following the eruption of Mount St. Helens.

9
00:00:21.590 --> 00:00:25.570
I visited it for the first time 20 years after, it was like a moonscape.

10
00:00:25.590 --> 00:00:27.490
A lot of it was still like a moonscape:

11
00:00:27.510 --> 00:00:30.140
you know, pieces of pumice on the ground, no vegetation.

12
00:00:30.160 --> 00:00:36.142
It has been a place of extraordinary change over the last forty years.

13
00:00:36.162 --> 00:00:36.560


14
00:00:36.580 --> 00:00:40.990
From really beautiful old growth forest to a moonscape.

15
00:00:41.010 --> 00:00:43.180
And then back again to a lot of unbroken

16
00:00:43.200 --> 00:00:48.680
sort-of twenty year-old forests, pretty high canopy cover.

17
00:00:48.700 --> 00:00:51.390
Uh, a lot of trees there now.

18
00:00:51.410 --> 00:00:57.460
From the fringes of the blast zone,

19
00:00:57.480 --> 00:01:00.220
you definitely see patterns of revegetation.

20
00:01:00.240 --> 00:01:03.740
They start slowly, with a little bit of greening,

21
00:01:03.760 --> 00:01:05.340
but by the time you get to the end of the time series,

22
00:01:05.360 --> 00:01:07.670
it looks pretty dark green. And you see the same thing on the ground.

23
00:01:07.690 --> 00:01:10.910
You see you know maybe not a forty year old forest,

24
00:01:10.930 --> 00:01:12.580
but something that looks thirty years old.

25
00:01:12.600 --> 00:01:17.660
And in this part of the country, trees are pretty tall after thirty years.

26
00:01:17.680 --> 00:01:22.320
What we’re looking at is Mount St. Helens

27
00:01:22.340 --> 00:01:26.670
in southwestern Washington, in 1973.

28
00:01:26.690 --> 00:01:29.270
Snow cover is what you see as white there,

29
00:01:29.290 --> 00:01:30.810
right in the middle of the mountain.

30
00:01:30.830 --> 00:01:35.090
It’s surrounded by some dark, deep reddish forests,

31
00:01:35.110 --> 00:01:40.320
which is basically how this MSS imagery sees older growth forests.

32
00:01:40.340 --> 00:01:45.060
To the east of it we se a lot of very active timber harvests.

33
00:01:45.080 --> 00:01:50.400
All of those patches of blue are recent clear cuts.

34
00:01:50.420 --> 00:01:52.820
Just to the north of the mountain, there,

35
00:01:52.840 --> 00:01:52.980
you see a very large clear cut.

36
00:01:53.000 --> 00:01:57.870
That one happens to be about two square miles,

37
00:01:57.890 --> 00:02:01.850
which is really really large by today’s standards.

38
00:02:01.870 --> 00:02:06.650
And then Spirit Lake, just to the northeast of the volcano.

39
00:02:06.670 --> 00:02:09.410
You will see that the shape of that lake will change,

40
00:02:09.430 --> 00:02:12.530
radically, after the volcano erupts.

41
00:02:12.550 --> 00:02:14.870
Well, in this image, I mean, if you remember that large clear cut

42
00:02:14.890 --> 00:02:21.040
that I pointed out you can see that it is starting to go from that bluish cast

43
00:02:21.060 --> 00:02:24.290
to having more red, which indicates, you know, recovery following harvest.

44
00:02:24.310 --> 00:02:30.287
And six years has passed, so you would definitely expect that

45
00:02:30.307 --> 00:02:32.390


46
00:02:32.410 --> 00:02:33.240
in a very productive forest like this one.

47
00:02:33.260 --> 00:02:38.340
And it has been joined by a lot more clear cuts in that area, too.

48
00:02:38.360 --> 00:02:41.440
I have looked at a lot of Landsat scenes.

49
00:02:41.460 --> 00:02:46.730
This is the biggest change from one image to another that I can think of.

50
00:02:46.750 --> 00:02:52.730
Forests and everything else, many miles to the north, were just incinerated.

51
00:02:52.750 --> 00:02:53.380


52
00:02:53.400 --> 00:02:58.920
The blast and the heat and the ash really levelled a lot.

53
00:02:58.940 --> 00:03:02.660
It looks from this image like Spirit Lake, just to the northeast of the volcano

54
00:03:02.680 --> 00:03:06.740
is not there, but it is there, it’s covered in logs.

55
00:03:06.760 --> 00:03:12.110
And most of the water in that lake got splashed up six hundred feet or more,

56
00:03:12.130 --> 00:03:17.220
and sort of dragged all of the trees that were on that wall down.

57
00:03:17.240 --> 00:03:19.880
Over the forty years since the eruption,

58
00:03:19.900 --> 00:03:23.010
you know, we do see that recovery happens first

59
00:03:23.030 --> 00:03:26.430
in the places that didn’t have that huge blast of heat

60
00:03:26.450 --> 00:03:31.950
and were not covered with many, many meters of ash or mud.

61
00:03:31.970 --> 00:03:36.270
In ’84, the first Thematic Mapper Landsat was launched.

62
00:03:36.290 --> 00:03:40.260
So that really changes our ability to display this kind of image

63
00:03:40.280 --> 00:03:44.520
in something closer to true color so it’s much more intuitive:

64
00:03:44.540 --> 00:03:46.100
green means green.

65
00:03:46.120 --> 00:03:50.420
So from this point forward you can sort of visualize

66
00:03:50.440 --> 00:03:52.360
the encroaching greenness

67
00:03:52.380 --> 00:03:58.359
which indicates the re-vegetating and re-foresting areas after the eruption.

68
00:03:58.379 --> 00:03:59.010


69
00:03:59.030 --> 00:04:04.460
Well, I’ll also point out some of the remaining old growth forest

70
00:04:04.480 --> 00:04:06.120
that you can see in that very dark patch.

71
00:04:06.140 --> 00:04:09.280
In the MSS imagery, that was dark red.

72
00:04:09.300 --> 00:04:12.600
It’s just much more intuitive to spot that kind of dark green

73
00:04:12.620 --> 00:04:15.780
when we can display it in true color.

74
00:04:15.800 --> 00:04:19.200
You can see in the early ‘90s clear cuts starting to pop up.

75
00:04:19.220 --> 00:04:24.170
So basically it looks like it is going from green

76
00:04:24.190 --> 00:04:30.175
to some kind of brownish color.

77
00:04:30.195 --> 00:04:32.950


78
00:04:32.970 --> 00:04:33.650
Even as the outer edge of these clearcuts are growing and filling in,

79
00:04:33.670 --> 00:04:38.390
the inner edges are greening up and turning green.

80
00:04:38.410 --> 00:04:40.290
And by the end of the time series they look pretty green,

81
00:04:40.310 --> 00:04:43.730
even though we just saw them get cut thirty years before that.

82
00:04:43.750 --> 00:04:45.990
So we have basically made a model

83
00:04:46.010 --> 00:04:51.360
that uses the imagery to predict what percent cover there is.

84
00:04:51.380 --> 00:04:54.830
Basically, how thick is the tree canopy here.

85
00:04:54.850 --> 00:04:57.900
And through the time series, you can see much of the blast zone

86
00:04:57.920 --> 00:05:00.750
going from red, which is zero trees,

87
00:05:00.770 --> 00:05:05.920
to pretty green, which is, you know, pretty solid tree cover.

88
00:05:05.940 --> 00:05:11.230
And that is really solid documentation of the recovery of the forest in this area.

89
00:05:11.250 --> 00:05:16.310
You can also see its neighboring places go from green to red

90
00:05:16.330 --> 00:05:20.450
in the opposite direction. Obviously there are harvests happening

91
00:05:20.470 --> 00:05:22.890
and those are taking away forest canopy

92
00:05:22.910 --> 00:05:26.870
at the same time that recovery is adding forest canopy

93
00:05:26.890 --> 00:05:30.770
in the place that was affected by the eruption.

94
00:05:30.790 --> 00:05:34.140
The really unique part about the Landsat record

95
00:05:34.160 --> 00:05:36.940
is the fact that it goes back to the ‘70s.

96
00:05:36.960 --> 00:05:41.420
I can’t imagine what it would be like to describe

97
00:05:41.440 --> 00:05:46.160
what this volcano did without having a time series of Landsat.

98
00:05:46.180 --> 00:05:51.180
We’ve got eight years before the eruption and forty years after the eruption.

99
00:05:51.200 --> 00:05:56.920
There is no other asset in the sky that can show us what Landsat does,

100
00:05:56.940 --> 00:06:00.290
in terms of the effect of the eruption

101
00:06:00.310 --> 00:06:04.210
and also the effect of the recovery following the eruption.

102
00:06:04.230 --> 00:06:09.060
Uh, it’s just amazingly lucky that Landsat was up there

103
00:06:09.080 --> 00:06:15.059
in its spot in the sky to watch this whole thing unfold.

104
00:06:15.079 --> 00:06:16.040


105
00:06:16.060 --> 00:00:00.000
Let’s hear it for Landsat.

106
00:00:00.000 --> 00:06:20.447