1 00:00:03,487 --> 00:00:09,087 Earth, a 4.5- Billion-year-old planet, still evolving. 2 00:00:09,087 --> 00:00:17,687 As continents shift and clash, volcanoes erupt, and glaciers grow and recede, 3 00:00:17,687 --> 00:00:23,127 the Earth's crust is carved in numerous and fascinating ways, 4 00:00:23,127 --> 00:00:26,039 leaving a trail of geological mysteries behind. 5 00:00:27,287 --> 00:00:31,917 In this episode, Krakatoa, one of the deadliest volcanoes in the world. 6 00:00:35,367 --> 00:00:39,487 More than 100 years ago, it erupted with such devastating fury 7 00:00:39,487 --> 00:00:43,287 that it wiped itself off the face of the Earth. 8 00:00:43,287 --> 00:00:47,121 In the process, it sent out the loudest sound in recorded history. 9 00:00:49,927 --> 00:00:53,363 And killed more than 36,000 people. 10 00:00:55,087 --> 00:00:58,363 And now, this deadly volcanic beast is back. 11 00:00:59,887 --> 00:01:04,927 Geologists investigate one of the world's fastest-growing volcanoes 12 00:01:04,927 --> 00:01:10,367 to hunt for clues that will tell them if, and when, Krakatoa will explode 13 00:01:10,367 --> 00:01:13,518 once again with the same cataclysmic force. 14 00:01:15,327 --> 00:01:17,927 As they prize apart the rocks, 15 00:01:17,927 --> 00:01:21,127 the answers they find will be another piece of the puzzle 16 00:01:21,127 --> 00:01:24,244 of how the Earth was made. 17 00:01:35,007 --> 00:01:40,767 Krakatoa is one of the most dangerous volcanoes the world has ever seen. 18 00:01:40,767 --> 00:01:44,447 When it exploded apart in 1883, 19 00:01:44,447 --> 00:01:48,326 the blast was heard over nearly 10% of the Earth's surface. 20 00:01:50,127 --> 00:01:52,807 It was a worldwide clarion call, 21 00:01:52,807 --> 00:01:56,887 announcing the awesome power of volcanoes. 22 00:01:56,887 --> 00:01:59,127 The site of this monstrous eruption 23 00:01:59,127 --> 00:02:02,847 lies between the Indonesian islands of Java and Sumatra, 24 00:02:02,847 --> 00:02:06,556 in a channel known as the Sunda Straits. 25 00:02:11,087 --> 00:02:17,087 Today, a new volcano has staked its claim in exactly the same spot. 26 00:02:17,087 --> 00:02:22,927 It's called Anak Krakatau, meaning "the child of Krakatoa". 27 00:02:22,927 --> 00:02:28,240 Right now, it's in the middle of a new and extremely dangerous phase. 28 00:02:30,087 --> 00:02:34,607 Dr Charles Mandeville travelled here to see if the child will one day be as deadly 29 00:02:34,607 --> 00:02:40,887 as its parent... to see if history is about to repeat itself. 30 00:02:40,887 --> 00:02:43,847 The stakes are high. 31 00:02:43,847 --> 00:02:48,007 At risk now are the one million people of Java and Sumatra 32 00:02:48,007 --> 00:02:51,682 who live within 50 miles of the volcano. 33 00:02:53,447 --> 00:02:57,607 MAN: Oh, wow. Look at that. We've got a little explosion going on. 34 00:02:57,607 --> 00:03:01,407 I've kind of been following this from the internet, from my office, 35 00:03:01,407 --> 00:03:04,638 but it's actually good to kind of see the thing, uh, live again. 36 00:03:05,887 --> 00:03:09,647 I've noticed in coming here that, uh, the volcano itself 37 00:03:09,647 --> 00:03:13,127 has grown possibly as much as 250 to 300 feet 38 00:03:13,127 --> 00:03:17,757 since the last time I've actually stood on its crater, back in 1990. 39 00:03:21,127 --> 00:03:24,047 Growing at a rate of 12 feet a year, 40 00:03:24,047 --> 00:03:28,887 the 1,033-foot volcano is both one of the fastest-growing 41 00:03:28,887 --> 00:03:32,482 and youngest volcanoes on the planet. 42 00:03:35,847 --> 00:03:42,687 This remarkable footage shows its explosive birth in June 1927, 43 00:03:42,687 --> 00:03:47,078 when it first broke through the sea floor and erupted out of the water. 44 00:03:48,527 --> 00:03:54,567 Its rapid growth is clear evidence that this new volcano is extremely active, 45 00:03:54,567 --> 00:03:57,639 but will it be as deadly as its parent? 46 00:04:02,807 --> 00:04:05,247 These eruptions are always accompanied 47 00:04:05,247 --> 00:04:08,807 by a series of ground-shaking tremors. 48 00:04:08,807 --> 00:04:12,807 For geologists, these small earthquakes are evidence that this volcano 49 00:04:12,807 --> 00:04:16,527 is entering a more destructive phase. 50 00:04:16,527 --> 00:04:19,727 Seismographs have been buried deep on Anak's slopes 51 00:04:19,727 --> 00:04:22,366 to record this underground activity. 52 00:04:23,367 --> 00:04:28,157 But these small quakes are not the only sign of a dangerously active volcano. 53 00:04:29,847 --> 00:04:33,847 A more subtle clue is right beneath Mandeville's feet. 54 00:04:33,847 --> 00:04:37,807 Black sand beaches are very common in volcanic areas. 55 00:04:37,807 --> 00:04:41,207 Uh, the minerals and the glass fragments that comprise the ash 56 00:04:41,207 --> 00:04:46,127 that the volcano erupts is typically dark charcoal grey coloured, 57 00:04:46,127 --> 00:04:50,567 and usually these materials don't stand up to weathering 58 00:04:50,567 --> 00:04:54,807 over long protracted periods of geologic time, 59 00:04:54,807 --> 00:04:58,527 but you find them in relatively fresh, pristine form 60 00:04:58,527 --> 00:05:00,597 when you are near an active volcano. 61 00:05:03,007 --> 00:05:07,047 Anak Krakatau is rarely completely quiet, 62 00:05:07,047 --> 00:05:10,527 but the level of activity in 2008 63 00:05:10,527 --> 00:05:14,236 shows that the volcano has become unusually violent. 64 00:05:17,167 --> 00:05:21,247 To discover just how much of a threat it could pose in the near future, 65 00:05:21,247 --> 00:05:23,927 volcano detectives must turn to their history books 66 00:05:23,927 --> 00:05:28,487 to learn what made its parent Krakatoa so destructive. 67 00:05:28,487 --> 00:05:33,087 This is a story that has fascinated geologists for over a century. 68 00:05:33,087 --> 00:05:35,127 What got me switched on to volcanology 69 00:05:35,127 --> 00:05:37,047 was the 1883 eruption, 70 00:05:37,047 --> 00:05:38,807 I learned about this at school, 71 00:05:38,807 --> 00:05:40,567 and I remember thinking how incredible 72 00:05:40,567 --> 00:05:43,087 that an island could just blow itself into oblivion. 73 00:05:43,087 --> 00:05:45,767 You know, what was going on? What was that all about? 74 00:05:45,767 --> 00:05:48,607 What was special? You know, how does that happen? 75 00:05:48,607 --> 00:05:50,677 And could it happen again elsewhere on Earth? 76 00:05:53,727 --> 00:05:56,967 Before it exploded in 1883, 77 00:05:56,967 --> 00:06:01,287 Krakatoa was an uninhabited island with three jagged peaks, 78 00:06:01,287 --> 00:06:03,278 covered in lush vegetation. 79 00:06:04,927 --> 00:06:07,367 It was part of the Dutch East Indies, 80 00:06:07,367 --> 00:06:11,679 a thriving, bustling hub of international trade. 81 00:06:13,167 --> 00:06:16,287 Indonesia's wealth of minerals and spices 82 00:06:16,287 --> 00:06:21,077 attracted many Western traders, journalists and geologists. 83 00:06:22,447 --> 00:06:25,847 Their reports provide first-hand accounts of what happened 84 00:06:25,847 --> 00:06:30,363 before and during Krakatoa's deadly and shocking eruption. 85 00:06:32,607 --> 00:06:36,885 There had been no hint of volcanic activity in anyone's memory. 86 00:06:39,647 --> 00:06:43,640 No-one had a clue that Krakatoa was about to blow. 87 00:06:44,687 --> 00:06:47,767 Beneath its green and placid surface, 88 00:06:47,767 --> 00:06:52,047 Krakatoa was a time bomb waiting to explode. 89 00:06:52,047 --> 00:06:54,687 So the first idea the locals would have got that anything was... 90 00:06:54,687 --> 00:06:56,767 ...anything strange was happening on their island 91 00:06:56,767 --> 00:06:58,487 would have been in May 1883. 92 00:06:58,487 --> 00:07:00,842 Earthquakes, earth tremors. 93 00:07:04,727 --> 00:07:08,367 These tremors reached as far as the capital Batavia, 94 00:07:08,367 --> 00:07:12,087 more than 100 miles away. 95 00:07:12,087 --> 00:07:15,287 Few suspected that the island of Krakatoa, 96 00:07:15,287 --> 00:07:18,167 seen on the distant horizon, was to blame, 97 00:07:18,167 --> 00:07:23,560 and that these earthquakes were the first clue to its deadly potential. 98 00:07:28,407 --> 00:07:35,597 Then, on May 20th, 1883, Krakatoa announced that it was no mere island. 99 00:07:39,247 --> 00:07:44,767 One of Krakatoa's three peaks exploded with extreme force, 100 00:07:44,767 --> 00:07:47,964 shooting a plume of ash hundreds of feet into the air. 101 00:07:51,287 --> 00:07:56,847 But after these initial fireworks, the activity appeared to cease. 102 00:07:56,847 --> 00:08:00,044 The local population breathed a sigh of relief. 103 00:08:01,567 --> 00:08:05,047 Thinking it safe, the governor of the Dutch East Indies sent 104 00:08:05,047 --> 00:08:08,487 a research party of geologists to the island in late May, 105 00:08:08,487 --> 00:08:10,847 where they observed the scorched landscape 106 00:08:10,847 --> 00:08:13,487 and smoking crater with amazement. 107 00:08:13,487 --> 00:08:18,407 Their meticulous report gives modern-day geologists the first clue 108 00:08:18,407 --> 00:08:21,922 as to what lay behind Krakatoa's immense power. 109 00:08:24,447 --> 00:08:28,007 A key discovery was a layer of pumice one foot deep 110 00:08:28,007 --> 00:08:30,396 that covered the island's shores. 111 00:08:31,887 --> 00:08:36,767 This pumice is the solidified lava that comes from the heart of a volcano, 112 00:08:36,767 --> 00:08:39,281 and it's riddled with bubbles. 113 00:08:40,287 --> 00:08:45,361 These bubbles suggest to geologists that Krakatoa is a stratovolcano. 114 00:08:46,407 --> 00:08:48,127 And those volcanoes tend to be 115 00:08:48,127 --> 00:08:49,967 the classic volcanoes that you see in textbooks, 116 00:08:49,967 --> 00:08:54,165 they're very steep-sided, like sort of sharp, almost triangular type mountains. 117 00:08:55,807 --> 00:09:00,327 These are the most dangerous types of volcanoes on Earth. 118 00:09:00,327 --> 00:09:03,807 They are fuelled by molten rock called lava, 119 00:09:03,807 --> 00:09:06,127 known as magma when it's underground. 120 00:09:06,127 --> 00:09:11,647 The magma that flows though these volcanoes is like liquid dynamite. 121 00:09:11,647 --> 00:09:15,487 Stratovolcanoes are dangerous because of the sorts of lava that they erupt, 122 00:09:15,487 --> 00:09:19,727 and the lava that comes out of stratovolcanoes is very sticky, 123 00:09:19,727 --> 00:09:23,687 viscous lava, and the danger there is that sticky lava 124 00:09:23,687 --> 00:09:25,803 often contains large amounts of gas. 125 00:09:28,087 --> 00:09:32,207 The bubbles inside the pumice discovered on Krakatoa in 1883 126 00:09:32,207 --> 00:09:37,042 show that the magma was once packed with explosive gases. 127 00:09:38,527 --> 00:09:40,847 Because the magma was so sticky - 128 00:09:40,847 --> 00:09:44,847 a term describing its thickness and resistance to flow - 129 00:09:44,847 --> 00:09:47,727 the gas could not easily escape. 130 00:09:47,727 --> 00:09:51,847 And the formation of gas bubbles in the sticky lava can be powerful enough 131 00:09:51,847 --> 00:09:54,287 to actually rip the lava apart, 132 00:09:54,287 --> 00:09:57,727 and, in the process, you actually tear away the volcano. 133 00:09:57,727 --> 00:09:59,687 The whole thing becomes... becomes explosive 134 00:09:59,687 --> 00:10:02,759 and you produce very dangerous volcanic activity. 135 00:10:04,807 --> 00:10:08,607 Krakatoa's magma had another deadly property. 136 00:10:08,607 --> 00:10:10,127 PETFORD: In some situations, 137 00:10:10,127 --> 00:10:13,367 the lava can become so sticky that it sort of freezes up 138 00:10:13,367 --> 00:10:18,887 and congests or chokes up the volcano, it forms a kind of a plug or a seal. 139 00:10:18,887 --> 00:10:20,847 What will happen is that, over time, 140 00:10:20,847 --> 00:10:24,247 more magma is coming up and being trapped beneath that plug. 141 00:10:24,247 --> 00:10:28,047 At some... some time in the future, the pressure will be so great 142 00:10:28,047 --> 00:10:30,247 that there'll be so much magma wanting to get up 143 00:10:30,247 --> 00:10:32,007 that you'll just rip the plug apart, 144 00:10:32,007 --> 00:10:34,805 and that can produce, again, a catastrophic volcanic eruption. 145 00:10:38,727 --> 00:10:44,677 This is exactly what happened at Krakatoa on May 20th, 1883. 146 00:10:46,287 --> 00:10:49,327 From then onwards, over the summer, it quietened down a bit, 147 00:10:49,327 --> 00:10:51,841 but this was really the kind of calm before the storm. 148 00:10:53,487 --> 00:10:56,887 The investigation into Krakatoa's deadly potential 149 00:10:56,887 --> 00:10:59,196 has produced important evidence. 150 00:11:00,567 --> 00:11:04,407 The frequent earthquakes on Anak Krakatau today indicate 151 00:11:04,407 --> 00:11:06,921 the volcano is still dangerous. 152 00:11:08,687 --> 00:11:13,727 The pumice from 1883 reveals that Krakatoa was a stratovolcano, 153 00:11:13,727 --> 00:11:18,084 its sticky, gas-rich lava making it dangerously explosive. 154 00:11:21,967 --> 00:11:26,407 Krakatoa's eruption in May 1883 was spectacular, 155 00:11:26,407 --> 00:11:29,763 but beneath the surface, Krakatoa was refuelling. 156 00:11:31,247 --> 00:11:37,004 An even greater eruption was gathering force out of sight and out of mind. 157 00:11:42,567 --> 00:11:47,447 Anak Krakatau is one of the fastest-growing volcanoes in the world. 158 00:11:47,447 --> 00:11:51,767 Geologists are investigating its threat to the region. 159 00:11:51,767 --> 00:11:56,921 They have turned to the past to uncover what made its parent so deadly. 160 00:12:00,527 --> 00:12:06,247 In 1883, exactly 100 days after Krakatoa first blew, 161 00:12:06,247 --> 00:12:09,922 the volcano showed its true power. 162 00:12:10,927 --> 00:12:14,927 This final phase of eruptions began at six minutes past one 163 00:12:14,927 --> 00:12:17,441 on the afternoon of August 26th. 164 00:12:24,807 --> 00:12:29,167 All three volcanic peaks erupted simultaneously, 165 00:12:29,167 --> 00:12:35,640 hurling dense clouds of ash and smoke an astonishing 17 miles into the sky. 166 00:12:37,647 --> 00:12:40,887 The eruption of Krakatoa was one of the... the biggest volcanic events 167 00:12:40,887 --> 00:12:42,647 of the last few hundred years, 168 00:12:42,647 --> 00:12:44,127 and it would have been, 169 00:12:44,127 --> 00:12:45,847 to people observing it, 170 00:12:45,847 --> 00:12:48,839 it would have been like the beginning of the end of the world, if you like. 171 00:12:51,127 --> 00:12:54,647 The power of this eruption was immense, 172 00:12:54,647 --> 00:12:57,807 like a giant jet engine aimed skywards. 173 00:12:57,807 --> 00:13:02,647 The air quickly became choked with tons of thick black ash, 174 00:13:02,647 --> 00:13:04,727 blotting out the sun. 175 00:13:04,727 --> 00:13:07,247 So the temperature, because of all the ash in the atmosphere, 176 00:13:07,247 --> 00:13:09,727 would be stifling, and if you were very near, 177 00:13:09,727 --> 00:13:11,767 on the, for example, the west coast of Java, 178 00:13:11,767 --> 00:13:14,127 you... you'd be getting the ash in your throat and in the eyes. 179 00:13:14,127 --> 00:13:16,925 It would have been, you know, a real vision of hell. 180 00:13:18,247 --> 00:13:22,167 And a nightmare that showed no signs of ending. 181 00:13:22,167 --> 00:13:26,127 By the next morning of August 27th 1883, 182 00:13:26,127 --> 00:13:30,803 Krakatoa's three craters had been raging for more than 14 hours. 183 00:13:34,567 --> 00:13:38,727 Then, sometime between 5:30 and 10:02am, 184 00:13:38,727 --> 00:13:44,996 the land was deafened by a series of four huge explosions. 185 00:13:46,327 --> 00:13:47,927 The noise was so loud, 186 00:13:47,927 --> 00:13:53,365 it could be heard over 2,000 miles away in the Australian desert near Perth. 187 00:13:55,967 --> 00:14:00,047 The third was the loudest recorded noise in history, 188 00:14:00,047 --> 00:14:03,407 the equivalent to 200 megatons of TNT, 189 00:14:03,407 --> 00:14:09,039 13,000 times the size of the bomb that destroyed Hiroshima. 190 00:14:14,087 --> 00:14:17,887 What created this awesome explosion? 191 00:14:17,887 --> 00:14:19,887 The hunt for answers 192 00:14:19,887 --> 00:14:22,247 takes geologist Charles Mandeville 193 00:14:22,247 --> 00:14:24,203 to the jagged island of Rakata. 194 00:14:26,407 --> 00:14:28,527 This tiny island is, in fact, 195 00:14:28,527 --> 00:14:30,597 a part of the once-mighty Krakatoa. 196 00:14:34,047 --> 00:14:37,007 The record of what the volcano did 197 00:14:37,007 --> 00:14:41,847 from May 20th to August 26th to 27th is here 198 00:14:41,847 --> 00:14:45,327 represented on the islands by the layered deposits 199 00:14:45,327 --> 00:14:48,127 that we see preserved in the jungle. 200 00:14:48,127 --> 00:14:50,567 This is a goldmine for a volcanologist 201 00:14:50,567 --> 00:14:52,367 trying to reconstruct the events 202 00:14:52,367 --> 00:14:56,207 that took place here, because each one of these deposits tells us 203 00:14:56,207 --> 00:15:00,166 something particular about what the volcano was doing. 204 00:15:01,487 --> 00:15:06,327 This pumice was thrown out of the heart of the volcano in 1883. 205 00:15:06,327 --> 00:15:10,767 Mandeville believes that it holds the key to understanding the forces 206 00:15:10,767 --> 00:15:13,687 that destroyed Krakatoa. 207 00:15:13,687 --> 00:15:18,567 What I have in my hand is a mixed pumice or streaked pumice. 208 00:15:18,567 --> 00:15:21,887 And what it represents is that we had two magmas 209 00:15:21,887 --> 00:15:26,403 mingling in the conduit of the 1883 eruption of Krakatoa. 210 00:15:28,087 --> 00:15:33,047 The stripes are proof of the two types of magma inside Krakatoa. 211 00:15:33,047 --> 00:15:36,927 The lighter band represents the cooler, gas-rich magma 212 00:15:36,927 --> 00:15:40,847 that was present during the earlier eruption in May. 213 00:15:40,847 --> 00:15:45,727 This eruption only partially emptied the magma chamber. 214 00:15:45,727 --> 00:15:49,367 By August, this void was filled from deep below 215 00:15:49,367 --> 00:15:53,367 by searingly hot, dark-coloured magma. 216 00:15:53,367 --> 00:15:58,367 When these two magmas mixed together, it was a lethal cocktail. 217 00:15:58,367 --> 00:16:02,167 The intense heat of the dark magma caused the huge amounts of gas 218 00:16:02,167 --> 00:16:04,681 within the light magma to expand. 219 00:16:05,807 --> 00:16:09,767 The magma chamber that was holding this mixed bag 220 00:16:09,767 --> 00:16:13,967 became overpressurised to the point where it exceeded the rock strength 221 00:16:13,967 --> 00:16:17,487 of the roof rocks above it, and when that happens, 222 00:16:17,487 --> 00:16:22,207 you can get really rapid ascent of magma to the surface. 223 00:16:22,207 --> 00:16:25,447 When this magma exploded from the surface, 224 00:16:25,447 --> 00:16:30,680 it ripped apart tons of rocks with an ear-splitting blast. 225 00:16:32,367 --> 00:16:37,521 This mega explosion caused the loudest noise in recorded history. 226 00:16:38,767 --> 00:16:43,567 The striped pumice on Rakata proves that magma mixing was the trigger. 227 00:16:43,567 --> 00:16:48,447 But Krakatoa wasn't just the loudest volcano in history. 228 00:16:48,447 --> 00:16:50,517 It was a killer. 229 00:16:52,727 --> 00:16:55,767 Because Krakatoa itself was uninhabited, 230 00:16:55,767 --> 00:16:59,607 some of the volcano's first victims were at Ketimbang, 231 00:16:59,607 --> 00:17:02,997 a village on the southern coast of Sumatra. 232 00:17:04,087 --> 00:17:08,447 But Ketimbang is on the mainland, 20 miles from Krakatoa, 233 00:17:08,447 --> 00:17:12,967 and separated by the waters of the Sunda Straits. 234 00:17:12,967 --> 00:17:17,882 How these people fell victim to the deadly ashes was a mystery. 235 00:17:19,047 --> 00:17:23,487 To uncover the answers, we have to return to the scene of the crime, 236 00:17:23,487 --> 00:17:27,639 Rakata, and to these imposing white cliffs. 237 00:17:28,687 --> 00:17:31,247 They may seem part of an ancient landscape, 238 00:17:31,247 --> 00:17:36,887 but these 200-foot white cliffs were laid down in a matter of hours. 239 00:17:36,887 --> 00:17:42,127 They are what's left of a raging torrent of hot gas and rocks - 240 00:17:42,127 --> 00:17:46,484 a terrifying force of nature known as a pyroclastic flow. 241 00:17:49,527 --> 00:17:53,247 Pyroclastic flows travel extremely quickly, so you can't outrun them. 242 00:17:53,247 --> 00:17:56,607 They're also extremely hot, several hundred degrees centigrade, 243 00:17:56,607 --> 00:17:58,647 so they will, if you're caught in the middle of one, 244 00:17:58,647 --> 00:18:00,399 they will incinerate you instantly. 245 00:18:04,007 --> 00:18:08,487 Perhaps the most famous victims of a pyroclastic flow lie at Pompeii, 246 00:18:08,487 --> 00:18:11,767 the Roman settlement that was utterly destroyed during the eruption 247 00:18:11,767 --> 00:18:15,362 of Vesuvius in Italy in the year 79. 248 00:18:17,047 --> 00:18:20,927 The perfectly preserved remains of the people here are testament 249 00:18:20,927 --> 00:18:23,680 to the power of these fiery avalanches. 250 00:18:25,247 --> 00:18:28,487 And most people die not because of 100% burns, 251 00:18:28,487 --> 00:18:31,287 but because they inhale the gases which are so hot 252 00:18:31,287 --> 00:18:34,647 that they just destroy the... the air passage and the lungs instantly, 253 00:18:34,647 --> 00:18:36,797 and so after two breaths, you're dead. 254 00:18:39,447 --> 00:18:43,967 The sheer size of the cliffs at Rakata have led geologists to estimate 255 00:18:43,967 --> 00:18:47,207 that the pyroclastic flows thrown out by Krakatoa 256 00:18:47,207 --> 00:18:51,567 were an amazing 2,800 feet high. 257 00:18:51,567 --> 00:18:54,207 But the victims of this deadly torrent 258 00:18:54,207 --> 00:18:57,807 were on the other side of the Sunda Straits. 259 00:18:57,807 --> 00:19:00,647 What happened next was truly astonishing. 260 00:19:00,647 --> 00:19:04,047 Pyroclastic flows are... are ground-hugging. 261 00:19:04,047 --> 00:19:06,727 In other words, they... they follow the ground surface as they go down. 262 00:19:06,727 --> 00:19:09,807 But they also have a... an upper part which is very rich in gas, 263 00:19:09,807 --> 00:19:11,527 so it's low density. 264 00:19:11,527 --> 00:19:13,927 Now, when a pyroclastic flow hits the sea, 265 00:19:13,927 --> 00:19:16,887 the dense bit carries on down onto the ocean bed, 266 00:19:16,887 --> 00:19:20,287 but the gas-rich but still very hot bit goes hurtling across, 267 00:19:20,287 --> 00:19:22,127 scooting across the top of the water, 268 00:19:22,127 --> 00:19:24,487 there's virtually no friction between the gas and the water 269 00:19:24,487 --> 00:19:26,478 so it can travel a very long distance. 270 00:19:27,727 --> 00:19:31,767 Over 2,000 people at Ketimbang perished from the burning debris 271 00:19:31,767 --> 00:19:35,327 that could not just walk on water but run, 272 00:19:35,327 --> 00:19:41,675 at amazing speeds of up to 200 miles per hour across 20 miles of open sea. 273 00:19:44,127 --> 00:19:47,047 The investigation into the Krakatoa volcano 274 00:19:47,047 --> 00:19:51,677 has pinpointed the extraordinary force that ripped the island apart. 275 00:19:54,247 --> 00:20:01,287 Striped pumice is proof that magma mixing created the vast explosion. 276 00:20:01,287 --> 00:20:07,407 200-foot cliffs on the island of Rakata are evidence of vast pyroclastic flows, 277 00:20:07,407 --> 00:20:12,561 big enough to cross the ocean and claim the volcano's first victims. 278 00:20:14,327 --> 00:20:16,527 But contemporary reports show 279 00:20:16,527 --> 00:20:21,487 that most of Krakatoa's victims were not killed by these deadly avalanches, 280 00:20:21,487 --> 00:20:25,844 but by a very different force of nature. 281 00:20:30,967 --> 00:20:36,405 August, 1883, Krakatoa's second and most deadly eruption. 282 00:20:37,767 --> 00:20:42,921 More than 2,000 people were killed by searingly hot pyroclastic flows. 283 00:20:44,127 --> 00:20:46,960 But there was worse to come. 284 00:20:48,247 --> 00:20:52,167 These gigantic boulders are on the shore of Anjer in Java, 285 00:20:52,167 --> 00:20:55,487 22 miles away from Krakatoa. 286 00:20:55,487 --> 00:20:59,487 They are a crucial clue to what the volcano did here, 287 00:20:59,487 --> 00:21:03,799 and a stark reminder of what could one day happen again. 288 00:21:04,967 --> 00:21:09,287 They are made of coral, which can only grow underwater. 289 00:21:09,287 --> 00:21:15,847 So, some immense force unleashed by Krakatoa must have put them here. 290 00:21:15,847 --> 00:21:19,887 These shattered bricks are another piece of the same puzzle. 291 00:21:19,887 --> 00:21:22,887 They are all that remain of a lighthouse 292 00:21:22,887 --> 00:21:27,367 that once was one of the sturdiest buildings on the Java coastline, 293 00:21:27,367 --> 00:21:30,207 but no match for Krakatoa. 294 00:21:30,207 --> 00:21:32,047 I'm standing at the top 295 00:21:32,047 --> 00:21:33,927 of the new lighthouse in Anjer, 296 00:21:33,927 --> 00:21:36,047 120ft above sea level, 297 00:21:36,047 --> 00:21:38,447 built two years after the eruption 298 00:21:38,447 --> 00:21:40,567 of Krakatoa in 1883. 299 00:21:40,567 --> 00:21:45,007 The old lighthouse down there is nothing but a trace of bricks, 300 00:21:45,007 --> 00:21:49,487 because it was wiped out by a large tsunami. 301 00:21:49,487 --> 00:21:55,167 Eyewitness accounts detail the exact height of this terrifying wave. 302 00:21:55,167 --> 00:21:57,567 Difficult though it might be to comprehend, 303 00:21:57,567 --> 00:22:02,047 the momentum of that wave would have taken the water up to the level 304 00:22:02,047 --> 00:22:04,047 that I am now standing. 305 00:22:04,047 --> 00:22:08,887 Krakatoa's death throes had triggered a massive wall of water 306 00:22:08,887 --> 00:22:12,007 that now raced towards the shore at Anjer. 307 00:22:12,007 --> 00:22:13,807 I don't think anyone living along the shores 308 00:22:13,807 --> 00:22:16,127 of western Java or southern Sumatra 309 00:22:16,127 --> 00:22:18,447 would have known about the tsunami 310 00:22:18,447 --> 00:22:19,967 that they were about to face, 311 00:22:19,967 --> 00:22:22,087 and, certainly, nobody would have been able to survive 312 00:22:22,087 --> 00:22:24,047 those sorts of wave heights. 313 00:22:24,047 --> 00:22:29,127 The power of the wave can be seen in this 600-ton block of coral 314 00:22:29,127 --> 00:22:33,200 that was ripped from the sea bed and smashed the lighthouse to pieces. 315 00:22:34,607 --> 00:22:38,527 Still here today, it provides some of the clearest evidence 316 00:22:38,527 --> 00:22:43,407 of the immense power of Krakatoa's 1883 eruption. 317 00:22:43,407 --> 00:22:46,447 The same wave that shifted this boulder 318 00:22:46,447 --> 00:22:50,007 also destroyed houses, villages and transport, 319 00:22:50,007 --> 00:22:53,682 leaving nothing but twisted wreckage behind. 320 00:22:55,807 --> 00:22:59,687 The mighty wave even picked up and stranded a Dutch steamer, 321 00:22:59,687 --> 00:23:02,599 the Berouw, two miles inland. 322 00:23:07,407 --> 00:23:12,435 This immense tsunami claimed the lives of more than 34,000 people. 323 00:23:14,167 --> 00:23:17,167 It's quite possible that those people who lived in the villages 324 00:23:17,167 --> 00:23:19,167 in western Java and southern Sumatra thought, 325 00:23:19,167 --> 00:23:20,927 "Well, the volcano's out there somewhere, 326 00:23:20,927 --> 00:23:23,127 "it's an island, so it can't possibly affect us here." 327 00:23:23,127 --> 00:23:25,767 But of course the... the eruption itself triggered the tsunami, 328 00:23:25,767 --> 00:23:28,247 which meant that the water adjacent to the volcano 329 00:23:28,247 --> 00:23:31,087 was... was being displaced right across to where they lived. 330 00:23:31,087 --> 00:23:35,763 So you know, that... that feeling of safety was... was sadly misplaced. 331 00:23:36,767 --> 00:23:40,967 For modern-day investigators, the puzzle was how fire and water 332 00:23:40,967 --> 00:23:44,407 had combined to wipe out an entire region. 333 00:23:44,407 --> 00:23:49,087 The evidence came from the shattered remains of the volcano itself, 334 00:23:49,087 --> 00:23:54,241 Rakata island, part of one of Krakatoa's three original peaks. 335 00:23:55,567 --> 00:23:58,287 Its sheer vertical cliff face 336 00:23:58,287 --> 00:24:02,485 tells volcano detectives about Krakatoa's final moments. 337 00:24:04,007 --> 00:24:07,927 When you have a very large volcanic eruption, you evacuate a lot of magma, 338 00:24:07,927 --> 00:24:09,807 it leaves behind, effectively, a hole, 339 00:24:09,807 --> 00:24:12,927 so quite often the crust just collapses down into that hole 340 00:24:12,927 --> 00:24:15,521 and that leaves behind what we call a caldera. 341 00:24:16,807 --> 00:24:21,567 Krakatoa had ejected such vast amounts of burning magma and rock, 342 00:24:21,567 --> 00:24:24,035 it could no longer support itself. 343 00:24:25,727 --> 00:24:29,367 Drain away the water and we can see how it collapsed, 344 00:24:29,367 --> 00:24:31,483 creating an immense caldera. 345 00:24:32,927 --> 00:24:37,447 So this cliff behind me marks the edge of the 1883 caldera. 346 00:24:37,447 --> 00:24:43,087 Under the boat, this water depth is about 40 times as deep 347 00:24:43,087 --> 00:24:45,647 as most of the area around us. 348 00:24:45,647 --> 00:24:48,407 Uh, the scale of this collapse is pretty big, 349 00:24:48,407 --> 00:24:52,167 it formed a caldera that's about three miles in the north-south direction 350 00:24:52,167 --> 00:24:55,364 by about five miles in the east-west direction. 351 00:24:57,327 --> 00:25:00,607 This immense collapse has only occurred once 352 00:25:00,607 --> 00:25:03,487 in recorded human history. 353 00:25:03,487 --> 00:25:09,167 The combined weight and power of Krakatoa's awesome pyroclastic flows 354 00:25:09,167 --> 00:25:13,843 and this huge collapse was more than enough to trigger the tsunami. 355 00:25:15,727 --> 00:25:20,327 The riddle of just what had caused Krakatoa's tremendous tsunamis 356 00:25:20,327 --> 00:25:22,636 had finally been solved. 357 00:25:25,607 --> 00:25:28,847 When the smoke had cleared and the waters receded 358 00:25:28,847 --> 00:25:32,047 from the most devastating eruption in recorded history, 359 00:25:32,047 --> 00:25:35,756 the island of Krakatoa had vanished. 360 00:25:37,167 --> 00:25:44,926 In total, Krakatoa had killed 36,417 men, women and children. 361 00:25:47,327 --> 00:25:52,196 It was, without doubt, one of the most dangerous volcanoes in history. 362 00:25:56,847 --> 00:26:00,047 But while investigating the 1883 eruption, 363 00:26:00,047 --> 00:26:05,883 scientists discovered ancient lava flows hidden in the jungle and on the sea bed. 364 00:26:08,127 --> 00:26:11,961 This deadly volcano had struck before. 365 00:26:13,087 --> 00:26:17,567 But when scientists dated the lava flows, they hit a problem. 366 00:26:17,567 --> 00:26:21,487 Radiocarbon dating was only able to place the eruption 367 00:26:21,487 --> 00:26:26,561 to between the first and 13th centuries - a spread of 1,200 years. 368 00:26:28,807 --> 00:26:33,007 Scientists needed more information in order to try and shed light 369 00:26:33,007 --> 00:26:35,127 on a new Krakatoa threat 370 00:26:35,127 --> 00:26:39,200 and help the hundreds of thousands of people living in the area. 371 00:26:43,527 --> 00:26:48,885 The trail of evidence at Krakatoa had gone cold... literally. 372 00:26:52,767 --> 00:26:56,927 Because, thousands of miles away from the sweltering heat of Indonesia, 373 00:26:56,927 --> 00:26:59,207 in the frozen wastes of the Antarctic, 374 00:26:59,207 --> 00:27:04,998 scientists recently discovered a critical clue to Krakatoa's explosive past. 375 00:27:07,407 --> 00:27:10,247 Well, ice cores are cylinders of ice that we drill from the ice caps 376 00:27:10,247 --> 00:27:11,847 in Greenland and Antarctica. 377 00:27:11,847 --> 00:27:13,487 You can look at things like volcanoes, um, 378 00:27:13,487 --> 00:27:15,327 any material coming from the surrounding oceans 379 00:27:15,327 --> 00:27:19,407 will make its way to Antarctica, where we can detect it in the ice. 380 00:27:19,407 --> 00:27:22,967 You might imagine that we see the dust and the ash from a volcano, 381 00:27:22,967 --> 00:27:26,687 but, in fact, very little of that from the big, um, Indonesian type volcanoes 382 00:27:26,687 --> 00:27:28,767 ever makes it to Antarctica. 383 00:27:28,767 --> 00:27:31,327 So what we do see is... is sulfuric acid, 384 00:27:31,327 --> 00:27:34,967 big volcanoes spew out a lot of sulfur dioxide into the atmosphere 385 00:27:34,967 --> 00:27:39,119 which is oxidised into the sulfuric acid, which we then measure in the ice. 386 00:27:40,327 --> 00:27:44,647 The sulfuric acid cannot be seen in the ice cores with the naked eye, 387 00:27:44,647 --> 00:27:48,447 but can only be detected back at the British Antarctic Survey's lab, 388 00:27:48,447 --> 00:27:54,238 where the cores are kept at a continuous minus 13 degrees Fahrenheit. 389 00:27:56,967 --> 00:27:59,207 So this is a... a piece of core from Antarctica. 390 00:27:59,207 --> 00:28:04,087 This is a piece from James Ross Island, it's about 10,000 years old, this ice. 391 00:28:04,087 --> 00:28:06,087 What we're doing now is measuring the volcanic signals, 392 00:28:06,087 --> 00:28:09,927 and what we see is very, very distinct, clear electrical pulses 393 00:28:09,927 --> 00:28:11,967 that come from the sulfuric acid from the volcanoes, 394 00:28:11,967 --> 00:28:14,447 so very quickly, we can see all the volcano signals 395 00:28:14,447 --> 00:28:16,367 throughout the whole core. 396 00:28:16,367 --> 00:28:20,207 One of the strongest signals found in the ice cores 397 00:28:20,207 --> 00:28:22,801 is from the 1883 eruption of Krakatoa. 398 00:28:23,967 --> 00:28:27,567 What we can see from the 1883 eruption, we can't see the ash, 399 00:28:27,567 --> 00:28:29,727 but we can see a very large peak in sulfuric acid, 400 00:28:29,727 --> 00:28:32,607 in fact it's one of the biggest peaks we've got in the last thousand years. 401 00:28:32,607 --> 00:28:35,647 It's such a big peak, in fact, that we use it to date the ice cores, 402 00:28:35,647 --> 00:28:38,115 because it's like a reference horizon that we can see there. 403 00:28:40,247 --> 00:28:43,927 Each ice core is like a diary of the Earth's climate. 404 00:28:43,927 --> 00:28:47,207 Each layer of ice represents one year. 405 00:28:47,207 --> 00:28:49,967 In the same way that we can count tree rings, 406 00:28:49,967 --> 00:28:52,927 scientists can count back each layer of ice 407 00:28:52,927 --> 00:28:56,967 to determine the exact date of any eruption. 408 00:28:56,967 --> 00:28:59,767 Counting back from the 1883 signal, 409 00:28:59,767 --> 00:29:05,767 there is a huge spike in the sulfuric acid levels in the year 535. 410 00:29:05,767 --> 00:29:09,007 This is clear evidence of an enormous eruption 411 00:29:09,007 --> 00:29:11,527 during the dying days of the Roman Empire - 412 00:29:11,527 --> 00:29:16,362 an eruption far greater than Krakatoa's in 1883. 413 00:29:18,447 --> 00:29:21,287 We are now beginning to come to the conclusion that, 414 00:29:21,287 --> 00:29:24,407 yes, there was a large volcanic eruption in 535. 415 00:29:24,407 --> 00:29:27,007 In fact, it looks one of the biggest ones on the record, 416 00:29:27,007 --> 00:29:30,487 in terms of how much sulfuric acid it put into the atmosphere. 417 00:29:30,487 --> 00:29:34,047 The ice cores tell us a lot about this mystery volcano. 418 00:29:34,047 --> 00:29:38,567 Its eruption was so enormous that its impact was global. 419 00:29:38,567 --> 00:29:42,487 Its date falls exactly in the middle of the timespan 420 00:29:42,487 --> 00:29:44,927 of the lava flows around Rakata. 421 00:29:44,927 --> 00:29:47,727 Could it be Krakatoa? 422 00:29:47,727 --> 00:29:49,727 The clues seemed to fit. 423 00:29:49,727 --> 00:29:51,367 If they are the same eruption, 424 00:29:51,367 --> 00:29:56,767 this is evidence that Krakatoa has a far more deadly past 425 00:29:56,767 --> 00:30:00,327 and, potentially, a far more deadly future. 426 00:30:00,327 --> 00:30:02,367 Can we tell whether it's come from Krakatoa? 427 00:30:02,367 --> 00:30:05,007 Now, that's more difficult, we can see it in Antarctica 428 00:30:05,007 --> 00:30:06,927 and we can see it in Greenland, 429 00:30:06,927 --> 00:30:09,647 so that tells us it was probably somewhere mid-latitude, 430 00:30:09,647 --> 00:30:13,487 so somewhere round about the equator, maybe, so it's a possibility, 431 00:30:13,487 --> 00:30:16,047 but we cannot really pin it down at the moment. 432 00:30:17,087 --> 00:30:18,727 Despite this uncertainty, 433 00:30:18,727 --> 00:30:22,720 there is no doubt of Krakatoa's capacity for destruction. 434 00:30:26,127 --> 00:30:29,767 The steep cliffs at Rakata show that Krakatoa collapsed 435 00:30:29,767 --> 00:30:34,767 to form an enormous caldera, triggering a deadly tsunami. 436 00:30:34,767 --> 00:30:37,127 And yet ice cores from Antarctica 437 00:30:37,127 --> 00:30:40,167 suggest that Krakatoa may have exploded before 438 00:30:40,167 --> 00:30:43,125 with even more force than 1883. 439 00:30:44,687 --> 00:30:48,927 To discover what originally created not only 1883 Krakatoa, 440 00:30:48,927 --> 00:30:51,127 but also the current Anak Krakatau, 441 00:30:51,127 --> 00:30:58,044 scientists will have to travel even further back in time, some two million years. 442 00:31:02,447 --> 00:31:06,647 The source of Krakatoa's awesome power remained a mystery to scientists 443 00:31:06,647 --> 00:31:08,205 for centuries. 444 00:31:10,647 --> 00:31:13,087 One clue is its location. 445 00:31:13,087 --> 00:31:17,927 Indonesia contains more volcanoes than anywhere else on Earth. 446 00:31:17,927 --> 00:31:21,407 Indonesia's a jackpot for volcanologists, 447 00:31:21,407 --> 00:31:25,167 simply because the evidence of volcanic centres 448 00:31:25,167 --> 00:31:27,887 that may have lasted several million years 449 00:31:27,887 --> 00:31:31,516 are available and ready for observation and study. 450 00:31:32,847 --> 00:31:38,327 Incredibly, there are 21 of these "fire mountains" on the island of Java alone - 451 00:31:38,327 --> 00:31:42,036 an area the same size as New York State. 452 00:31:44,007 --> 00:31:46,967 The National Park of Tennger Bromo in east Java 453 00:31:46,967 --> 00:31:50,880 is one of Indonesia's most active volcanic zones. 454 00:31:52,047 --> 00:31:55,727 To view a landscape like this is actually humbling, 455 00:31:55,727 --> 00:31:58,847 because it tells us that there are forces at work 456 00:31:58,847 --> 00:32:03,796 that far exceed anything that mankind can construct. 457 00:32:04,847 --> 00:32:09,367 But why there should be so many volcanoes in such a small area, 458 00:32:09,367 --> 00:32:10,720 no-one could explain. 459 00:32:12,247 --> 00:32:18,047 A key discovery was that Indonesia lies adjacent to the notorious Ring of Fire, 460 00:32:18,047 --> 00:32:22,677 a chain of volcanoes stretching around the entire Pacific Ocean. 461 00:32:25,847 --> 00:32:30,727 In the 1950s, American geologist Harry Hess began research 462 00:32:30,727 --> 00:32:35,247 into the groundbreaking hypothesis known as sea floor spreading. 463 00:32:35,247 --> 00:32:38,637 This laid the foundation for plate tectonics. 464 00:32:40,327 --> 00:32:42,407 Plate tectonics is based on the idea 465 00:32:42,407 --> 00:32:45,967 that our planet is not a perfect and unbroken sphere. 466 00:32:45,967 --> 00:32:50,567 It's composed of eight major tectonic plates that jostle and jar 467 00:32:50,567 --> 00:32:52,007 against one another. 468 00:32:52,007 --> 00:32:56,398 These plates are driven by heat from the planet's core. 469 00:33:00,847 --> 00:33:02,287 Here in Indonesia, 470 00:33:02,287 --> 00:33:06,485 the plates collide faster than almost anywhere else on Earth. 471 00:33:08,047 --> 00:33:12,207 The volcanoes here are created when the heavier oceanic plate 472 00:33:12,207 --> 00:33:14,960 is pushed under the lighter continental rock. 473 00:33:17,927 --> 00:33:20,236 This is subduction. 474 00:33:21,447 --> 00:33:25,767 When the rock is pushed deeper, it melts to produce magma. 475 00:33:25,767 --> 00:33:30,207 Over thousands of years, it builds up into a vast magma chamber, 476 00:33:30,207 --> 00:33:33,727 many miles beneath the surface of the Earth. 477 00:33:33,727 --> 00:33:38,047 Eventually, the pressure of the extra magma becomes too great 478 00:33:38,047 --> 00:33:39,767 for the Earth's crust. 479 00:33:39,767 --> 00:33:42,887 The magma forces its way up to the surface 480 00:33:42,887 --> 00:33:45,355 in a storm of hot ash and boiling lava. 481 00:33:48,167 --> 00:33:50,442 A volcano is born. 482 00:33:53,047 --> 00:33:55,167 In the case of Indonesia, 483 00:33:55,167 --> 00:34:00,082 this is a nation constructed almost entirely from volcanoes. 484 00:34:01,127 --> 00:34:05,607 Most of Indonesia is, in fact, composed of volcanoes 485 00:34:05,607 --> 00:34:09,247 that initiated from somewhere down below sea level, 486 00:34:09,247 --> 00:34:15,087 rose up to sea level and then grew as islands and amalgamated 487 00:34:15,087 --> 00:34:20,241 to form bigger land masses that now comprise the Indonesian nation. 488 00:34:21,247 --> 00:34:26,162 Using the theory of plate tectonics, scientists can rewind the clock. 489 00:34:28,367 --> 00:34:34,247 45 million years ago, the Australian plate started to move north rapidly. 490 00:34:34,247 --> 00:34:38,327 The island chain of Indonesia began to emerge from the ocean 491 00:34:38,327 --> 00:34:41,046 at the point where the two plates collided. 492 00:34:42,167 --> 00:34:45,287 Vast numbers of volcanoes exploded 493 00:34:45,287 --> 00:34:50,047 as the Australian plate was pushed deep into the bowels of the Earth. 494 00:34:50,047 --> 00:34:54,247 Krakatoa was a product of these same forces, 495 00:34:54,247 --> 00:34:57,127 and it was two million years ago, 496 00:34:57,127 --> 00:35:01,087 as our early human ancestors were taking their first tentative steps, 497 00:35:01,087 --> 00:35:04,397 that the volcano was created. 498 00:35:05,887 --> 00:35:09,127 So the fact that under the Sunda Straits of Indonesia 499 00:35:09,127 --> 00:35:10,807 you have all these processes 500 00:35:10,807 --> 00:35:15,607 taking place 70 and 80 miles down below the surface 501 00:35:15,607 --> 00:35:20,767 made it inevitable that a volcano like Krakatoa came into existence, 502 00:35:20,767 --> 00:35:24,885 but also had a catastrophic eruption. 503 00:35:26,127 --> 00:35:29,247 What made Krakatoa so much more dangerous 504 00:35:29,247 --> 00:35:35,047 than hundreds of other volcanoes in Indonesia only became clear in 1988. 505 00:35:35,047 --> 00:35:39,727 Scientists discovered that large clusters of earthquakes were taking place 506 00:35:39,727 --> 00:35:42,447 beneath the Sunda Straits. 507 00:35:42,447 --> 00:35:45,927 Earthquakes are common along plate boundaries, 508 00:35:45,927 --> 00:35:49,287 but this amount was off the charts. 509 00:35:49,287 --> 00:35:52,167 This major clue would enable scientists 510 00:35:52,167 --> 00:35:55,921 to finally identify the killer factor in Krakatoa. 511 00:36:00,127 --> 00:36:03,367 Beneath Krakatoa, in the middle of the Sunda Straits, 512 00:36:03,367 --> 00:36:06,727 the subduction zone contains a kink. 513 00:36:06,727 --> 00:36:09,847 This twists and rips the Earth's crust, 514 00:36:09,847 --> 00:36:15,365 and provides even more material to fuel Krakatoa's hungry magma chamber. 515 00:36:17,047 --> 00:36:20,167 Where you have those kinks, two things could happen. 516 00:36:20,167 --> 00:36:22,567 Firstly there might be a greater chance of earthquakes 517 00:36:22,567 --> 00:36:25,967 because the kink itself actually starts to tear or rip, 518 00:36:25,967 --> 00:36:31,327 and secondly, where the kink is might generate more melting, 519 00:36:31,327 --> 00:36:33,447 and it's the melting that takes place in the mantle 520 00:36:33,447 --> 00:36:35,727 that ultimately leads to the lavas 521 00:36:35,727 --> 00:36:38,321 that are erupted from the volcanoes at the surface. 522 00:36:40,047 --> 00:36:43,960 Finally, the origins of Krakatoa had been revealed. 523 00:36:46,127 --> 00:36:48,887 Hundreds of volcanoes in Indonesia 524 00:36:48,887 --> 00:36:52,887 show that the country lies on a volatile plate boundary. 525 00:36:52,887 --> 00:36:59,207 Unusually high numbers of quakes show that Krakatoa lies on a deadly kink 526 00:36:59,207 --> 00:37:00,606 within this zone. 527 00:37:02,207 --> 00:37:07,487 But can scientists now use this knowledge to predict Krakatoa's future? 528 00:37:07,487 --> 00:37:10,727 A prediction that is today more important than ever, 529 00:37:10,727 --> 00:37:15,642 because the volcano is back, and it's getting bigger every day. 530 00:37:26,967 --> 00:37:30,287 Today, these shattered islands are all that remain 531 00:37:30,287 --> 00:37:34,280 of the cataclysmic 1883 Krakatoa eruption. 532 00:37:37,887 --> 00:37:42,287 But a deeper understanding of this event is now more important than ever, 533 00:37:42,287 --> 00:37:46,280 because, out in the Straits, a new threat is growing. 534 00:37:50,807 --> 00:37:54,407 Krakatoa is back, in the form of Anak Krakatau, 535 00:37:54,407 --> 00:37:58,687 Indonesian for "child of Krakatoa". 536 00:37:58,687 --> 00:38:03,044 And that child is now an angry teenager. 537 00:38:05,767 --> 00:38:07,367 Like a phoenix from the ashes, 538 00:38:07,367 --> 00:38:13,447 Anak Krakatau is growing directly over the site of the original Krakatoa volcano, 539 00:38:13,447 --> 00:38:17,847 leading scientists to conclude it's being fed by the same magma chamber 540 00:38:17,847 --> 00:38:21,367 deep beneath the Sunda Straits. 541 00:38:21,367 --> 00:38:25,327 This deadly heritage means that Anak could potentially be 542 00:38:25,327 --> 00:38:28,807 one of the most dangerous volcanoes on Earth. 543 00:38:28,807 --> 00:38:32,356 But just how immediate is this threat? 544 00:38:35,287 --> 00:38:39,007 Since its explosive beginnings in 1927, 545 00:38:39,007 --> 00:38:42,687 Anak has erupted frequently and violently. 546 00:38:42,687 --> 00:38:46,367 As one of the fastest-growing volcanoes on the planet, 547 00:38:46,367 --> 00:38:50,519 this 1,033-foot-high mountain bears watching. 548 00:38:53,087 --> 00:38:57,767 Predicting exactly when another major eruption will happen is difficult, 549 00:38:57,767 --> 00:39:00,207 but there are clues. 550 00:39:00,207 --> 00:39:05,207 Underground tremors are a sure sign that the magma deep within the volcano 551 00:39:05,207 --> 00:39:06,765 is starting to move. 552 00:39:07,807 --> 00:39:11,967 We have seismometers stationed on the volcano 553 00:39:11,967 --> 00:39:14,927 that tell us when rocks are breaking, 554 00:39:14,927 --> 00:39:18,167 not just at the vent, but in the subsurface, 555 00:39:18,167 --> 00:39:23,967 heralding the arrival of new, fresh magma into the edifice, into the cone. 556 00:39:23,967 --> 00:39:29,567 These details are transmitted via radio signals to the monitoring station 557 00:39:29,567 --> 00:39:33,647 on the mainland, which is operated 24 hours a day. 558 00:39:33,647 --> 00:39:39,167 They have a simple scale to measure the threat, running from one to five. 559 00:39:39,167 --> 00:39:42,637 Anything above a three, and they go on red alert. 560 00:39:45,127 --> 00:39:50,281 At the moment, it's hovering around the danger zone, a level three. 561 00:39:51,367 --> 00:39:54,527 The type of magma within the volcano is another way 562 00:39:54,527 --> 00:39:57,758 geologists can judge the potential of a major eruption. 563 00:39:59,047 --> 00:40:01,847 But the magma itself is impossible to test, 564 00:40:01,847 --> 00:40:05,607 as it lies several miles deep within the Earth. 565 00:40:05,607 --> 00:40:11,398 The next best clue is to look at what has been literally thrown out of the volcano. 566 00:40:12,807 --> 00:40:15,687 Lava bombs. 567 00:40:15,687 --> 00:40:19,287 I've got my hand on a basaltic andesite scoria bomb 568 00:40:19,287 --> 00:40:23,367 that was probably blown out of a vent about three quarters of a mile from here, 569 00:40:23,367 --> 00:40:27,847 and you can imagine, to be hit by one of these would not be a good situation. 570 00:40:27,847 --> 00:40:29,807 These can actually range up to things 571 00:40:29,807 --> 00:40:33,167 that are the size of refrigerators and television sets, 572 00:40:33,167 --> 00:40:36,087 and there... thereby making them even more lethal, 573 00:40:36,087 --> 00:40:39,443 particularly when they are travelling at 120 miles an hour. 574 00:40:41,927 --> 00:40:46,007 Mandeville analyses these rocks made up of basaltic andesite, 575 00:40:46,007 --> 00:40:47,687 which will give him a clue 576 00:40:47,687 --> 00:40:49,882 to the make-up of the magma deep underground. 577 00:40:51,367 --> 00:40:56,367 Part of what, uh, this composition tells me is the composition of magmas 578 00:40:56,367 --> 00:41:00,207 being erupted at Anak are unlike what was typically erupted 579 00:41:00,207 --> 00:41:03,887 at, uh, the 1883 eruption of Krakatoa, 580 00:41:03,887 --> 00:41:08,567 which was much more silica-rich and much lighter in colour, 581 00:41:08,567 --> 00:41:11,718 typically light beige to almost white. 582 00:41:13,247 --> 00:41:18,527 The more silica in the magma, the more viscous, or sticky, it is. 583 00:41:18,527 --> 00:41:23,965 And that's what contributed to Krakatoa's explosive eruption in 1883. 584 00:41:26,487 --> 00:41:29,967 The explosive gases were trapped in the magma 585 00:41:29,967 --> 00:41:32,959 and pressure had been building up over time. 586 00:41:34,247 --> 00:41:38,247 Fortunately, the dark colour of the lava bombs from Anak Krakatau 587 00:41:38,247 --> 00:41:43,207 are evidence that the magma is low in silica, 588 00:41:43,207 --> 00:41:48,804 and the explosive gases have yet to reach critical 1883 levels. 589 00:41:49,847 --> 00:41:53,527 But this is not a permanent state. 590 00:41:53,527 --> 00:41:58,807 Over the years, a magma like this can, in fact, evolve 591 00:41:58,807 --> 00:42:01,196 into something that was that explosive. 592 00:42:03,527 --> 00:42:09,567 As Anak Krakatau grows, the magma will certainly become thicker and stickier. 593 00:42:09,567 --> 00:42:13,527 As in its parent, once the magma gets too sticky, 594 00:42:13,527 --> 00:42:16,087 the vent could become blocked. 595 00:42:16,087 --> 00:42:19,124 The silence could signal disaster. 596 00:42:20,327 --> 00:42:23,607 It means that pressure could be building up inside. 597 00:42:23,607 --> 00:42:25,567 Too much pressure, 598 00:42:25,567 --> 00:42:29,640 and Indonesia could suffer another cataclysmic explosion. 599 00:42:36,167 --> 00:42:39,687 More than 100 years of investigation into Krakatoa 600 00:42:39,687 --> 00:42:42,807 has helped unlock the secrets of its past 601 00:42:42,807 --> 00:42:45,847 and provided scientists with strong evidence 602 00:42:45,847 --> 00:42:49,920 that Anak Krakatau is following in its footsteps. 603 00:42:51,727 --> 00:42:57,359 The pumice from 1883 suggests that Krakatoa was a deadly stratovolcano. 604 00:42:58,967 --> 00:43:02,927 The stripes in the pumice show that the massive 1883 eruption 605 00:43:02,927 --> 00:43:06,447 was triggered by an injection of superhot magma. 606 00:43:06,447 --> 00:43:10,440 It was this that blew the volcano to pieces. 607 00:43:11,887 --> 00:43:15,127 The remains of vast pyroclastic flows 608 00:43:15,127 --> 00:43:18,367 that were over twice the height of the Empire State Building, 609 00:43:18,367 --> 00:43:20,887 plus the immense caldera, 610 00:43:20,887 --> 00:43:26,287 show the massive scale of Krakatoa's 1883 eruption. 611 00:43:26,287 --> 00:43:28,967 But most ominously of all, 612 00:43:28,967 --> 00:43:33,047 the position of Anak Krakatau near the deadly Ring of Fire 613 00:43:33,047 --> 00:43:36,327 directly above a kink in the subduction zone 614 00:43:36,327 --> 00:43:39,683 means that a future massive eruption is inevitable. 615 00:43:41,767 --> 00:43:46,527 A lot of the Anak Krakatau activity that we now witness today 616 00:43:46,527 --> 00:43:50,247 is actually almost a continuation of the volcanic activity 617 00:43:50,247 --> 00:43:52,727 that took place back in 1883. 618 00:43:52,727 --> 00:43:54,847 We could have another eruption here 619 00:43:54,847 --> 00:43:58,476 on the scale of the 1883 eruption of Krakatoa. 620 00:43:59,487 --> 00:44:03,687 The 1883 eruption of Krakatoa may be the most famous, 621 00:44:03,687 --> 00:44:07,807 but it is a geological certainty that it won't be the last. 622 00:44:07,807 --> 00:44:10,767 Krakatoa is on the rise again, 623 00:44:10,767 --> 00:44:14,885 dynamic proof that the Earth is never at rest.