WEBVTT 1 00:00:38.600 --> 00:00:46.480 Three days ago, these lava flows erupted in fiery fountains. 2 00:00:49.520 --> 00:00:54.640 Materials thrown up from the earth's interior have transformed this land. 3 00:01:09.060 --> 00:01:16.260 Now rising water vapor and hot gases are the only signs of activity at the volcano's vent. 4 00:01:18.040 --> 00:01:27.580 While the lava is still hot beneath its crust, scientists arrive to investigate the effects of the eruption. We will join them. 5 00:01:37.800 --> 00:01:49.880 Portable seismometers and a recording seismograph are set up to monitor the volcano. The seismograph shows that activity continues below the surface. 6 00:01:49.880 --> 00:02:02.500 The National Bureau of Standards, WWDH, Maui, Hawaii. Next tone begins at 21 hours 15 minutes. Greenwich Mean Time. 7 00:02:08.060 --> 00:02:17.580 Some equipment has been destroyed by the lava flow. Long sections of cable must be replaced. 8 00:02:22.200 --> 00:02:27.340 Cable is laid across the new lava, beyond which a seismometer is positioned. 9 00:02:29.680 --> 00:02:39.860 By cable, signals from the seismometer are transmitted to the Hawaiian Volcano Observatory, staffed by scientists of the United States Geological Survey. 10 00:02:52.260 --> 00:03:00.240 Here, movements of the active volcano are continuously recorded, a clue to the dynamic forces within the earth. 11 00:03:03.260 --> 00:03:18.320 On the island of Hawaii are two of the world's largest volcanoes, Mauna Kea and Mauna Loa. East of Mauna Loa is Kilauea, one of the earth's most studied active volcanoes. 12 00:03:18.320 --> 00:03:25.400 The activity we are investigating is on the east rift zone of Kilauea. 13 00:03:30.100 --> 00:03:32.840 Fifteen kilometers away is Kilauea's summit. 14 00:03:39.520 --> 00:03:51.220 At the summit, overlooking the caldera, is the volcano observatory. From the observatory, cables go out to seismometers strategically placed around the mountain. 15 00:03:52.740 --> 00:04:01.020 Sensor signals are transmitted to the observatory, where a bank of seismographs continuously records them. 16 00:04:05.220 --> 00:04:08.340 Here we see the tracing during a relatively quiet period. 17 00:04:17.720 --> 00:04:21.220 The needle crosses a previously recorded earthquake. 18 00:04:21.220 --> 00:04:40.800 Suddenly, a new earthquake occurs, indicating movement of the volcano. Most of these earthquakes can only be detected by sensitive seismometers. They cannot be felt by man. 19 00:05:00.140 --> 00:05:09.800 Tracings for a 24-hour period reveal frequent earthquakes, as many as 50 to 100 a day of differing magnitudes. 20 00:05:16.460 --> 00:05:25.800 The shaking of an earthquake lasts only a short time, but harmonic tremor may go on for days. 21 00:05:26.980 --> 00:05:31.440 Harmonic tremor is probably caused by the movement of magma within the volcano. 22 00:05:32.720 --> 00:05:37.760 Movement of magma may also cause changes in the shape of the volcano. 23 00:05:39.500 --> 00:05:47.580 Changes in the tilt of the mountain slopes are measured with a sensitive leveling instrument, set up at the center of a triangle. 24 00:05:47.580 --> 00:05:57.040 The corners of the triangle are marked by calibrated rods. 25 00:05:59.500 --> 00:06:09.720 A change in the tilt of the land will move the rods up or down in relation to one another. These changes are detected by the leveling instrument. 26 00:06:11.520 --> 00:06:22.460 A tent protects the instrument from the influences of direct sunlight and wind. Tilt triangles are set up at many locations on the volcano. 27 00:06:29.640 --> 00:06:35.740 In weather of all kinds, repeated measurements of the tilt are made at each triangle. 28 00:06:37.480 --> 00:06:42.420 From these measurements, calculations are made to show changes in the volcano's shape. 29 00:06:45.000 --> 00:06:56.960 The results plotted on a graph show that during the last eruption, the volcano deflated rapidly, but that since then it has started to inflate once more. 30 00:07:03.300 --> 00:07:08.120 As the swelling continues, hot gases are observed at the vent. 31 00:07:10.180 --> 00:07:16.480 This degassing provides a rare opportunity to gather samples of gases from within the volcano. 32 00:07:21.820 --> 00:07:27.780 Gases pass through metal tubing into a collecting jar. 33 00:07:27.780 --> 00:07:35.060 The vent is closely watched. 34 00:07:37.100 --> 00:07:42.100 Degassing accompanied by lava spatter may suddenly increase. 35 00:08:12.100 --> 00:08:15.720 As swelling continues, the summit caldera expands. 36 00:08:19.060 --> 00:08:25.240 To measure the expansion, a geotometer is positioned over a permanent marker on one side of the caldera. 37 00:08:27.800 --> 00:08:35.260 A beam of light is directed at a reflector on the opposite side of the caldera, five kilometers away. 38 00:08:40.360 --> 00:08:48.880 By measuring the travel time of light, the geotometer detects changes in this distance as small as a few millimeters. 39 00:08:56.360 --> 00:09:03.640 Calculations show that the geotometer stations on the summit have moved apart several centimeters since the last eruption. 40 00:09:10.340 --> 00:09:14.740 Further evidence that the volcano is inflating. 41 00:09:19.360 --> 00:09:24.700 A few days later, observers at the vent report lava is rising. 42 00:09:37.080 --> 00:09:42.080 The mounting activity is immediately reported to the observatory by radio. 43 00:10:12.340 --> 00:10:18.720 As pressure continues to build within the volcano, lava overflows the vent. 44 00:10:59.860 --> 00:11:06.420 Fifteen minutes later, the lava flows back into the vent, ending a short eruptive cycle. 45 00:11:06.420 --> 00:11:27.520 The volcano erupts. 46 00:11:32.520 --> 00:11:43.540 Though small in scale, this activity provides many of the features of a major eruption and a hint of what is to come. 47 00:11:46.840 --> 00:11:54.420 Later, the portable seismographs show increasing harmonic tremor. 48 00:12:00.500 --> 00:12:08.560 At some locations, the needle swings wide. At others, the tracing narrows. 49 00:12:09.920 --> 00:12:14.280 Data from several stations are plotted on a map and compared. 50 00:12:16.820 --> 00:12:22.560 The data show that the greatest activity is closest to station number one, near the vent. 51 00:12:25.500 --> 00:12:28.960 Continuing measurements suggest that molten rock is moving. 52 00:12:33.800 --> 00:12:37.060 Overnight, lava forms a spatter cone at the vent. 53 00:12:39.080 --> 00:12:42.540 Observers keep a close watch on the activity. 54 00:13:00.360 --> 00:13:06.160 Lava gushes from the vent, flows only a few meters, and pours back into the vent. 55 00:13:06.160 --> 00:13:25.580 The observers are in constant radio contact with the observatory, where seismographs record a sharp increase in earthquake activity. 56 00:13:25.580 --> 00:13:31.160 Tilt and geotometer measurements show the mountain is still swelling. 57 00:15:31.160 --> 00:15:34.940 After five hours, Kilauea has been in violent eruption. 58 00:15:38.120 --> 00:15:55.560 The height of the fountain is constantly measured. 59 00:15:55.560 --> 00:16:09.480 It has reached heights of 200 to 300 meters and is still rising. 60 00:16:19.100 --> 00:16:24.180 Smaller vents have opened. Lava spreads for kilometers around the site. 61 00:16:58.420 --> 00:17:03.100 Hawaiian lava is one of the hottest and most fluid in the world. 62 00:17:08.900 --> 00:17:11.980 A mighty river of lava has formed. 63 00:17:46.480 --> 00:17:51.840 The cascade, a curtain of fire, is twice as high as Niagara Falls. 64 00:17:53.660 --> 00:17:59.860 The fountain soars to heights of 500 meters, taller than the Empire State Building. 65 00:18:32.560 --> 00:18:39.180 After nine hours of activity, the fountain begins to subside. 66 00:18:42.960 --> 00:18:46.800 Rivers of lava still feed the falls. 67 00:19:04.120 --> 00:19:13.680 The main fountain dies. Lava flows back into the vent. 68 00:19:13.680 --> 00:19:23.760 One of the most spectacular eruptions in Hawaiian history has ended. 69 00:19:23.760 --> 00:19:36.400 The next tone begins at 15 hours, 20 minutes.