WEBVTT 00:00:13.880 --> 00:00:20.430 Ta'u is the easternmost island in the Samoan chain that has outcropping of basalt that 00:00:20.430 --> 00:00:25.330 actually relates to the Samoan hotspot. 00:00:25.330 --> 00:00:34.390 There is evidence that a large landslide occurred in the south side of Ta’u. 00:00:34.390 --> 00:00:40.160 If you look at the shape the morphology of Ta’u island you’ll see that on the north 00:00:40.160 --> 00:00:44.700 slope of the island is a relatively shallow slope. 00:00:44.700 --> 00:00:52.510 By contrast, the south side of the island you have this near vertical wall and this 00:00:52.510 --> 00:00:56.320 vertical wall is more than a thousand feet high. 00:00:56.320 --> 00:01:03.910 You have this incredible sense that a lot of mass is missing and our reason for believing 00:01:03.910 --> 00:01:11.540 that is that preliminary sonar imagery of the ocean floor shows inexplicably large blocks 00:01:11.540 --> 00:01:16.610 almost like a debris field thats directly beneath and to the south of the south side 00:01:16.610 --> 00:01:26.170 of Ta'u. Flank failure on the south side of Ta'u would be devastating for the region. 00:01:26.170 --> 00:01:29.700 The greatest energy would be focused to the south so the largest tsunamis would be generated 00:01:29.700 --> 00:01:33.939 due south of Samoa, but the energy travels radially. 00:01:33.939 --> 00:01:39.450 The waves traveling to the west would be expected to be hundreds of meters high, certainly by 00:01:39.450 --> 00:01:43.869 the time they encounter Ofu and maybe many tens of meters high by the time they encounter 00:01:43.869 --> 00:01:47.439 Tutuila and Upolu. 00:01:47.439 --> 00:01:53.939 But there is no real modern example for this in modern human history. 00:01:53.939 --> 00:01:59.209 The mechanism that is responsible for generating most of the tsunamis in the Samoan region 00:01:59.209 --> 00:02:05.060 would be the large scale mega thrust earthquakes that occur just to the south of us along the 00:02:05.060 --> 00:02:07.710 Tonga Trench. 00:02:07.710 --> 00:02:11.880 We have an example from two thousand nine. 00:02:19.200 --> 00:02:25.860 It was my first time in my life I had ever personally witnessed the devastation of a 00:02:25.900 --> 00:02:29.440 tsunami. 00:02:29.480 --> 00:02:36.880 It's always hard to guess the future. 00:02:36.880 --> 00:02:43.580 But the Samoans are almost certainly going to experience more large tsunamis in the future. 00:02:43.580 --> 00:02:49.040 Just because these islands are situated near a seduction zone thats generates the highest 00:02:49.040 --> 00:02:51.820 frequency of large mega earthquakes on earth. 00:02:51.820 --> 00:02:54.530 So they are always going to face that issue. 00:02:54.530 --> 00:02:59.920 The question is what other potential hazards do they face in the region. 00:02:59.920 --> 00:03:05.040 What what other mechanisms exist for generating large tsunamis in the region and the potential 00:03:05.040 --> 00:03:11.750 certainly exists for flank failures on some of the islands Ta'u and possibly Savai'i to 00:03:11.750 --> 00:03:13.550 generate tsunamis in the future. 00:03:13.550 --> 00:03:17.320 We have some evidence we need more evidence of course that tsunamis may have been generated 00:03:17.320 --> 00:03:23.810 by flank failure of Ta'u in the past. 00:03:23.810 --> 00:03:29.480 This cruise will provide us with the potential to evaluate whether or not submarine landslides 00:03:29.480 --> 00:03:31.460 have caused tsunamis in the past. 00:03:31.460 --> 00:03:37.100 We really don't have good maps of the debris fields located to the south of Ta'u. 00:03:37.100 --> 00:03:38.280 Those are really needed. 00:03:38.280 --> 00:03:46.230 These are really the missing link in this whole hypothesis that the south side of Ta'u 00:03:46.230 --> 00:03:50.890 is missing a big chunk of land as the result of flank failure in the volcano. 00:03:50.890 --> 00:03:53.600 So what we need to do is look for the missing pieces. 00:03:53.600 --> 00:03:57.320 If it's the result of flank failure, you've got see the rubble to the south of Ta'u. 00:03:57.320 --> 00:03:59.370 We need better maps to see if the rubble is there.