1 00:00:04,160 --> 00:00:07,240 This is Geology Bites with Oliver Strimpel. 2 00:00:08,760 --> 00:00:12,280 Water is strongly implicated in many of the most powerful 3 00:00:12,280 --> 00:00:16,560 volcanic eruptions. In this episode, we'll talk 4 00:00:16,560 --> 00:00:19,440 about the two main ways in which this comes about. 5 00:00:20,440 --> 00:00:24,000 The first is when magma comes into contact with external 6 00:00:24,000 --> 00:00:28,080 water, whether from oceans, groundwater, or glaciers. 7 00:00:28,920 --> 00:00:31,880 The second is when water is already present within the 8 00:00:31,880 --> 00:00:35,560 magma. Michael Manga studies how 9 00:00:35,560 --> 00:00:39,400 geological processes affect and are affected by water. 10 00:00:40,360 --> 00:00:43,520 He also studies similar processes on other planets and 11 00:00:43,520 --> 00:00:45,960 on the icy moons of the outer solar system. 12 00:00:46,960 --> 00:00:49,920 He is a professor in the Earth and Planetary Science Department 13 00:00:49,920 --> 00:00:52,000 of the University of California, Berkeley. 14 00:00:53,120 --> 00:00:55,320 Michael Manga. Welcome to Geology Bites. 15 00:00:55,760 --> 00:00:57,680 Oliver, it's a pleasure to join you today. 16 00:00:58,120 --> 00:01:01,400 Let's talk about the first of the two ways that water effects 17 00:01:01,400 --> 00:01:06,240 eruptions, the so-called friato magmatic eruptions, when 18 00:01:06,400 --> 00:01:09,360 external water and hot magma come into contact. 19 00:01:09,960 --> 00:01:13,760 How does this amplify the explosive power of an eruption? 20 00:01:14,160 --> 00:01:16,400 Yeah, you highlighted in that question, Oliver, something 21 00:01:16,400 --> 00:01:18,760 that's really important. Actually, maybe we should define 22 00:01:18,760 --> 00:01:22,080 the word friato magmatic. Friato means water. 23 00:01:22,640 --> 00:01:26,800 Magmatic refers to the melted rock, and the key is that 24 00:01:26,800 --> 00:01:31,080 Magma's hot and water is cold, and so heat is transferred from 25 00:01:31,080 --> 00:01:35,480 hot objects to cold bodies. And so as the magma cools down, 26 00:01:35,560 --> 00:01:37,280 it becomes brittle and it breaks. 27 00:01:37,800 --> 00:01:39,640 And maybe if some of your listeners have had this 28 00:01:39,640 --> 00:01:42,200 unfortunate opportunity of putting some water into hot 29 00:01:42,200 --> 00:01:44,440 glass and it shatters as it cools too quickly. 30 00:01:45,200 --> 00:01:47,920 And so this will make the small pieces of magma that become 31 00:01:47,920 --> 00:01:50,640 volcanic ash that can erupt explosively. 32 00:01:51,480 --> 00:01:54,440 The water in turn, of course, it's cooling the magma, but it's 33 00:01:54,440 --> 00:01:57,680 heating up because it's taking that heat and liquid water 34 00:01:57,680 --> 00:02:02,000 becomes steam, and steam takes up much more space than the 35 00:02:02,000 --> 00:02:04,640 liquid water did. And so that huge volume 36 00:02:04,640 --> 00:02:07,720 expansion, as it expands, carries with it the fragmented 37 00:02:07,720 --> 00:02:10,800 magma, volcanic ash with it as it expands. 38 00:02:11,720 --> 00:02:14,680 You know, most physical systems that we think about, we have 39 00:02:14,680 --> 00:02:17,360 motion that I guess you can think of as being kinetic 40 00:02:17,360 --> 00:02:19,280 energy. When you rub your hands 41 00:02:19,280 --> 00:02:21,640 together, your hands are moving, they have kinetic energy. 42 00:02:22,520 --> 00:02:26,240 And if that energy is dissipated to make heat, when your hands 43 00:02:26,240 --> 00:02:28,080 are rubbing against each other, that's friction. 44 00:02:28,880 --> 00:02:32,320 And so most processes in the Earth take kinetic energy and 45 00:02:32,320 --> 00:02:34,880 convert them into heat. What's special about 46 00:02:34,880 --> 00:02:38,360 freyatomagmatic eruptions is the energy transfer goes the other 47 00:02:38,360 --> 00:02:40,480 way. We can take the heat in the 48 00:02:40,480 --> 00:02:44,320 magma and convert it into kinetic energy to make these 49 00:02:44,320 --> 00:02:49,240 eruptions so explosive. So because, as you said, when 50 00:02:49,240 --> 00:02:54,600 water turns to steam, there's a huge increase in volume, can 51 00:02:54,640 --> 00:02:58,320 steam therefore be generated even when the magma contacts 52 00:02:58,320 --> 00:03:02,200 water at great depths and therefore under great pressure 53 00:03:02,200 --> 00:03:04,920 under the ocean? So as we go deeper inside the 54 00:03:04,920 --> 00:03:08,120 earth or deeper under the surface of the ocean, the 55 00:03:08,120 --> 00:03:11,200 pressure goes up. And as pressure goes up, gases 56 00:03:11,200 --> 00:03:13,400 contract. And this matters for two 57 00:03:13,400 --> 00:03:16,680 reasons. First, liquid water at high 58 00:03:16,680 --> 00:03:18,600 pressures doesn't convert into steam. 59 00:03:18,600 --> 00:03:21,400 It doesn't boil. It becomes a supercritical 60 00:03:21,400 --> 00:03:23,760 liquid. And the second effect of higher 61 00:03:23,760 --> 00:03:26,600 pressure is that the boiling temperature goes up as well. 62 00:03:27,080 --> 00:03:30,080 So at the bottom of the ocean, when water can boil, it can be 63 00:03:30,080 --> 00:03:34,920 as hot as 400°C, and it can be very difficult for magma to heat 64 00:03:34,920 --> 00:03:38,240 water up to that temperature. And so the high pressure inside 65 00:03:38,240 --> 00:03:40,680 the Earth has two effects. It increases the boiling 66 00:03:40,680 --> 00:03:43,920 temperature and in fact can keep boiling from happening. 67 00:03:44,240 --> 00:03:46,760 And if you don't boil water, you don't have the big volume 68 00:03:46,760 --> 00:03:49,240 expansion that drives explosive eruption. 69 00:03:49,480 --> 00:03:52,960 And So what happens instead is that when you get pillow lavas 70 00:03:52,960 --> 00:03:54,080 forming? Yeah. 71 00:03:54,080 --> 00:03:56,000 Pillow lavas. The name is very descriptive. 72 00:03:56,000 --> 00:03:59,920 You see these little blobs of lava that look like pillows, 73 00:03:59,920 --> 00:04:02,520 hence their name. And those are wrapped in a style 74 00:04:02,520 --> 00:04:05,800 we call effusive. Effusive means lava flowing over 75 00:04:05,800 --> 00:04:09,200 the surface in a sort of a coherent, intact manner as 76 00:04:09,200 --> 00:04:12,160 opposed to breaking up into little pieces or fragmenting, 77 00:04:12,440 --> 00:04:14,600 which is what happens for explosive eruptions. 78 00:04:15,120 --> 00:04:18,320 And so pillow lavas form when low viscosity magmas are 79 00:04:18,320 --> 00:04:21,600 extruded onto the bottom of the ocean and they cool pretty 80 00:04:21,600 --> 00:04:24,320 quickly, which is why they get the pillow shape as opposed to 81 00:04:24,320 --> 00:04:27,240 making the very thick lava flows we see on land. 82 00:04:28,200 --> 00:04:31,400 So that interaction with water action in submarine settings to 83 00:04:31,400 --> 00:04:34,680 make pillow lavas is still very important by cooling the outside 84 00:04:34,680 --> 00:04:37,960 of the lava, but it does suppress explosive eruption. 85 00:04:38,560 --> 00:04:43,960 In 2022, we experienced the most powerful eruption in recent 86 00:04:44,040 --> 00:04:47,080 memory, and that was the Hunga Tonga eruption. 87 00:04:47,880 --> 00:04:51,600 Can you describe that eruption and compare it to other 88 00:04:51,600 --> 00:04:55,080 eruptions, just to put it in context, such as the Mount Saint 89 00:04:55,080 --> 00:04:59,960 Helen's eruption in 1980 or Mount Pinatubo 1991? 90 00:05:00,520 --> 00:05:05,160 And I guess water must have been implicated in that one. 91 00:05:05,360 --> 00:05:08,480 Yeah. So the hunger eruption of 2022 92 00:05:08,880 --> 00:05:11,920 was the most powerful volcanic eruption in our lifetimes. 93 00:05:12,200 --> 00:05:15,480 It was so powerful, people in Alaska, 8000 kilometers away 94 00:05:15,480 --> 00:05:18,040 could hear it. And the plume reached a height 95 00:05:18,040 --> 00:05:21,360 of 57 kilometers, which is higher than any eruption we have 96 00:05:21,360 --> 00:05:24,120 documented. Set a record for the number of 97 00:05:24,120 --> 00:05:26,960 lightning strikes. Just like thunderstorms create 98 00:05:26,960 --> 00:05:30,080 lightning, volcanic eruptions will also create lightning by 99 00:05:30,200 --> 00:05:33,760 very rapidly carrying ice and magma to great height. 100 00:05:34,480 --> 00:05:37,320 Also, this eruption created global tsunamis through a 101 00:05:37,320 --> 00:05:42,640 coupling between the atmosphere, the ocean and the solid part of 102 00:05:42,640 --> 00:05:44,080 the earth. And it was, of course, 103 00:05:44,080 --> 00:05:46,400 devastating for the Kingdom nation of Tonga. 104 00:05:47,440 --> 00:05:50,880 So it was an extremely powerful eruption, and much of the power 105 00:05:50,880 --> 00:05:54,280 was because it was a shallow submarine eruption, so that 106 00:05:54,280 --> 00:05:58,560 magma fragmented underwater, and those fragments can interact 107 00:05:58,560 --> 00:06:00,880 with the surrounding liquid water to make steam. 108 00:06:01,360 --> 00:06:03,480 And because the pressure is pretty low, it was a shallow 109 00:06:03,480 --> 00:06:05,120 eruption. A lot of steam could be 110 00:06:05,120 --> 00:06:09,720 generated, and that steam helped power the great energy of the 111 00:06:09,720 --> 00:06:12,120 eruption. You asked about how to put this 112 00:06:12,120 --> 00:06:15,880 in context. You and I were alive during the 113 00:06:15,880 --> 00:06:18,200 1980 Mount Saint Helens eruption. 114 00:06:18,840 --> 00:06:21,280 This eruption was 10 times bigger than Mount Saint Helens 115 00:06:21,280 --> 00:06:25,120 was and was similar to the Pinatubo eruption in the 116 00:06:25,120 --> 00:06:28,640 Philippines. It is small, though, in 117 00:06:28,640 --> 00:06:31,080 comparison with some of the biggest eruptions we know about 118 00:06:31,080 --> 00:06:34,040 what we call super eruptions, the ones that make things like 119 00:06:34,040 --> 00:06:36,720 the big calderas we see in Yellowstone National Park. 120 00:06:37,520 --> 00:06:41,800 About 10 years before the Hunger Tonga eruption, there was 121 00:06:41,800 --> 00:06:45,800 another eruption called the Harva eruption, not too, too far 122 00:06:45,800 --> 00:06:48,360 away, but that had a very different outcome. 123 00:06:48,360 --> 00:06:50,480 Can you tell us about that? Absolutely. 124 00:06:50,480 --> 00:06:53,920 And the Haver submarine eruption occurred South of Hunga Hunga 125 00:06:54,120 --> 00:06:56,720 along a volcanic arc. Volcanic arcs are produced when 126 00:06:56,720 --> 00:06:58,880 plates sink into the Earth's mantle. 127 00:06:59,560 --> 00:07:03,360 And the northern part of the subduction zone is the Tonga 128 00:07:03,360 --> 00:07:05,200 arc. The Kermadec arc is South of 129 00:07:05,200 --> 00:07:09,120 that, just north of New Zealand. And Haver eruption is in the 130 00:07:09,120 --> 00:07:12,000 Kermadec arc and it erupted in 2012. 131 00:07:12,000 --> 00:07:13,760 It was a deeper submarine eruption. 132 00:07:14,240 --> 00:07:18,240 The vent was 900 meters below the ocean surface, and that's 133 00:07:18,240 --> 00:07:21,280 deep enough that the way the volcano erupted was 134 00:07:21,280 --> 00:07:22,920 fundamentally really quite different. 135 00:07:23,080 --> 00:07:25,560 It was also smaller, although bigger than Mount Saint Helens 136 00:07:25,560 --> 00:07:29,240 once again was in 1980. If we call this a deep submarine 137 00:07:29,240 --> 00:07:32,840 eruption, the Haver eruption, it was the largest deep submarine 138 00:07:32,840 --> 00:07:37,240 eruption since 1650, and it created a raft of floating 139 00:07:37,240 --> 00:07:39,440 pumice. Pumice is a volcanic rock full 140 00:07:39,440 --> 00:07:42,320 of bubbles, and there's enough bubbles in this rock that the 141 00:07:42,440 --> 00:07:44,680 fragments can float on the ocean surface. 142 00:07:44,800 --> 00:07:48,000 And it created a huge raft of floating pumice and that 143 00:07:48,000 --> 00:07:51,280 promised because it floats, circumnavigates the planet with 144 00:07:51,280 --> 00:07:53,880 the ocean currents eventually washing up on beaches. 145 00:07:54,680 --> 00:07:56,520 The eruption style, though, is quite different. 146 00:07:56,640 --> 00:08:00,600 The magma as it entered the ocean from the volcanic vent was 147 00:08:00,600 --> 00:08:03,880 full of bubbles, but it hadn't yet fragmented and so it was 148 00:08:03,880 --> 00:08:05,920 extruded or squeezed into the ocean. 149 00:08:06,360 --> 00:08:08,440 There are enough bubbles in it that it's lighter than the 150 00:08:08,440 --> 00:08:12,160 ocean, so the magma floated up to the ocean surface and as it 151 00:08:12,160 --> 00:08:15,440 interacted with the surrounding water, the magma quenched. 152 00:08:15,440 --> 00:08:18,520 It cooled very quickly and broke up into the pieces of pumice 153 00:08:18,520 --> 00:08:21,840 that float on the ocean. Since we're in my office today, 154 00:08:21,840 --> 00:08:23,880 I can show you a piece of the pumice if that would be of 155 00:08:23,880 --> 00:08:25,800 interest. Yeah, please. 156 00:08:25,920 --> 00:08:30,240 So your listeners probably can't see, but these are two pieces I 157 00:08:30,240 --> 00:08:33,480 collected in New Zealand, were transported long distance for a 158 00:08:33,480 --> 00:08:36,159 long time. And unlike most things that 159 00:08:36,159 --> 00:08:39,559 break, they're not angular, but they're rounded on the sides. 160 00:08:40,039 --> 00:08:41,919 And they're rounded because these pieces of pumice, as they 161 00:08:41,919 --> 00:08:45,000 float on the ocean surface, are rubbing against each other, you 162 00:08:45,000 --> 00:08:46,440 know, kind of like pebbles on a beach. 163 00:08:46,440 --> 00:08:50,400 And so they get progressively rounder and smaller as well. 164 00:08:51,040 --> 00:08:53,880 And of course, you can't feel them to see how light they are. 165 00:08:54,560 --> 00:08:56,440 But I do have a container of water. 166 00:08:57,080 --> 00:08:59,560 And if, you know, I put it on, put the piece of pumice on the 167 00:08:59,560 --> 00:09:01,960 water. You can see that it floats. 168 00:09:01,960 --> 00:09:04,360 High and dry. And of course, it has to float 169 00:09:04,400 --> 00:09:05,520 right? It got all the way to New 170 00:09:05,520 --> 00:09:09,120 Zealand from the volcanic vent. And this pumice will float for 171 00:09:09,120 --> 00:09:11,160 years and years. You know, the thing we're 172 00:09:11,160 --> 00:09:13,800 learning about submarine eruptions that I guess we hadn't 173 00:09:13,800 --> 00:09:17,360 properly appreciated, not having had the chance to witness 174 00:09:17,800 --> 00:09:21,080 submarine eruptions and especially deep winds until 175 00:09:21,080 --> 00:09:25,160 2012, is that ocean depth is fundamentally important. 176 00:09:25,760 --> 00:09:29,720 At high depths, you suppress fragmentation, but fragments are 177 00:09:29,720 --> 00:09:31,840 still lighter than water, so they can float on the ocean 178 00:09:31,840 --> 00:09:33,920 surface. At shallow depths you have an 179 00:09:33,920 --> 00:09:37,400 explosive eruption surrounded by liquid water and you can get 180 00:09:37,400 --> 00:09:41,120 very explosive eruptions, more explosive than we had previously 181 00:09:41,120 --> 00:09:45,200 anticipated. Roughly what depth do we switch 182 00:09:45,200 --> 00:09:50,680 over from these highly explosive steam eruptions to the the more 183 00:09:50,680 --> 00:09:53,720 contained ones that either form pillows or the pumice? 184 00:09:54,400 --> 00:09:56,960 Yeah, that's an interesting question that I have actually 185 00:09:56,960 --> 00:09:59,760 tried to think about. How do we map depth onto 186 00:09:59,760 --> 00:10:02,960 eruption style? So let's go from the deepest to 187 00:10:02,960 --> 00:10:06,880 the shallowest. The critical pressure for water 188 00:10:07,520 --> 00:10:10,400 to form steam is about 2200 meters. 189 00:10:11,000 --> 00:10:15,320 So deeper than 2200 meters you should expect mostly effusive 190 00:10:15,320 --> 00:10:17,800 eruptions. And the average depth of mid 191 00:10:17,800 --> 00:10:21,880 ocean Ridge is where oceanic crust is formed is 2500 meters. 192 00:10:22,600 --> 00:10:25,480 The details of what that critical depth is depends on the 193 00:10:25,480 --> 00:10:28,280 eruption rate, how fast the Magma's erupting, and weather 194 00:10:28,280 --> 00:10:30,960 can fragment. But for the Haver eruption in 195 00:10:30,960 --> 00:10:35,160 2012 that formed the raft of floating pumice, if the vent was 196 00:10:35,160 --> 00:10:39,560 probably shallower than two or 300 meters, it probably would 197 00:10:39,560 --> 00:10:42,280 have been an explosive eruption, much like Hunga. 198 00:10:43,040 --> 00:10:44,960 And that's probably useful for hazard assessment. 199 00:10:45,240 --> 00:10:47,680 You can look at the volcanoes around the Earth and identify 200 00:10:47,680 --> 00:10:52,080 those in submarine settings that are below sea level or could 201 00:10:52,080 --> 00:10:54,880 become below sea level if they were to erupt. 202 00:10:55,640 --> 00:11:01,960 Are there some cases where eruptions start below that 2200m 203 00:11:01,960 --> 00:11:06,040 threshold, but because they produce so much lava they build 204 00:11:06,040 --> 00:11:10,520 up a kind of seamount and then get to that critical height and 205 00:11:10,520 --> 00:11:12,520 then stop to become steam driven? 206 00:11:13,480 --> 00:11:18,280 The answer is yes, that any volcano we see poking out of the 207 00:11:18,280 --> 00:11:21,720 ocean had to start its life below sea level. 208 00:11:22,120 --> 00:11:25,320 The islands on Hawaii are good examples where the tops of the 209 00:11:25,320 --> 00:11:28,720 mountains are way above sea level, high enough that there's 210 00:11:28,720 --> 00:11:32,320 even little glaciers on the tallest peaks on on Hawaii. 211 00:11:33,200 --> 00:11:36,760 And so those volcanoes grew from being in a deep submarine 212 00:11:36,760 --> 00:11:40,520 setting to a shallow submarine setting, to being above land. 213 00:11:42,000 --> 00:11:45,240 And the converse is true too, as volcanoes erupt and the flanks 214 00:11:45,240 --> 00:11:48,800 collapse what was once above sea level that then can migrate 215 00:11:48,800 --> 00:11:51,520 below sea level. Yeah, but you're not likely to 216 00:11:51,520 --> 00:11:55,120 go from a great depth to less than 2200 meters of depth in a 217 00:11:55,120 --> 00:11:57,320 single eruption. You're talking about a sequence 218 00:11:57,320 --> 00:11:59,440 of eruptions over many years. Yeah. 219 00:11:59,440 --> 00:12:03,640 To grow a volcano a kilometer in height will take a long time, 220 00:12:03,800 --> 00:12:06,960 probably many eruptions. And I don't know any good 221 00:12:06,960 --> 00:12:09,760 examples where we have documented the detailed growth 222 00:12:09,760 --> 00:12:11,840 of a volcanic edifice under the ocean. 223 00:12:12,800 --> 00:12:15,440 That question highlights one of the challenges in understanding 224 00:12:15,440 --> 00:12:19,080 submarine eruption is that to look at them and observe them, 225 00:12:19,080 --> 00:12:23,040 we have to go under the ocean because our cameras don't look 226 00:12:23,040 --> 00:12:26,080 below the ocean. And that requires sending either 227 00:12:26,080 --> 00:12:30,000 autonomous vehicles or remotely operated vehicles, or using 228 00:12:30,000 --> 00:12:33,600 sonar, some kind of remote mapping technology, to 229 00:12:33,600 --> 00:12:37,120 repeatedly survey the sea floor. It's not something we can 230 00:12:37,120 --> 00:12:43,680 monitor easily and continuously. Is this effect I have magma 231 00:12:44,120 --> 00:12:50,040 contacting external water? Also, what drives geysers, Hot 232 00:12:50,040 --> 00:12:54,400 Springs and mud volcanoes? So geysers are a special type of 233 00:12:54,400 --> 00:12:57,200 hot spring. They erupt boiling water, and 234 00:12:57,200 --> 00:13:00,040 they erupt episodically. And so when they do erupt, 235 00:13:00,040 --> 00:13:03,480 they're erupting a mixture of liquid water and water vapor or 236 00:13:03,480 --> 00:13:05,720 steam. Although actually geyser 237 00:13:05,720 --> 00:13:09,240 eruptions can be energetic enough to carry with them little 238 00:13:09,240 --> 00:13:12,120 fragments of rock. There's almost a continuum 239 00:13:12,120 --> 00:13:15,240 between geyser eruptions and hydrothermal explosions. 240 00:13:15,240 --> 00:13:19,120 Where hydrothermal explosion means hydro water explosion, 241 00:13:19,280 --> 00:13:21,720 things break apart and rock fragments get ejected. 242 00:13:21,800 --> 00:13:25,520 All the geyser fields that we know of, their energy source is 243 00:13:25,520 --> 00:13:30,080 in fact magma underground. So there's no magma directly 244 00:13:30,160 --> 00:13:34,080 erupting in the geyser, but the heat source is in fact Magnus 245 00:13:34,080 --> 00:13:37,000 that are solidifying and cooling underground, transferring their 246 00:13:37,000 --> 00:13:38,880 heat to the groundwater. So. 247 00:13:38,880 --> 00:13:42,720 When you get an intermittent eruption of a geyser, it's the 248 00:13:42,720 --> 00:13:46,320 periodic passage of some water over this magma. 249 00:13:46,880 --> 00:13:50,280 So when we look at a geyser erupting, we're seeing the very 250 00:13:50,280 --> 00:13:54,720 surficial manifestation of that heat transport deeper down. 251 00:13:54,800 --> 00:13:57,360 The groundwater flow that's carrying that heat is probably 252 00:13:57,360 --> 00:14:01,200 much more steady. And the water that's taking the 253 00:14:01,200 --> 00:14:03,880 heat out of the Magnus is probably circulating to depths 254 00:14:03,880 --> 00:14:07,000 of many hundreds of meters to even a few kilometers, and 255 00:14:07,000 --> 00:14:09,240 carrying that heat up to more shallow depths. 256 00:14:09,520 --> 00:14:12,040 Various reservoirs. And actually, from studies of 257 00:14:12,040 --> 00:14:16,120 geysers, direct imaging with cameras or using geophysical 258 00:14:16,120 --> 00:14:19,600 measurements beneath geysers, it looks like there are cavities in 259 00:14:19,600 --> 00:14:24,040 which heat and steam accumulate. In fact, that may be analogous 260 00:14:24,040 --> 00:14:26,960 to the reservoirs in which magma accumulates leading up to 261 00:14:26,960 --> 00:14:28,960 eruption. So actually, there are some 262 00:14:28,960 --> 00:14:33,240 similarities between geyser eruptions and volcanic eruptions 263 00:14:33,240 --> 00:14:35,440 in that they're episodic. They're not erupting 264 00:14:35,440 --> 00:14:38,040 continuously. And there are reservoirs that 265 00:14:38,040 --> 00:14:41,880 are accumulating the gases and the materials that erupt and the 266 00:14:41,880 --> 00:14:44,040 heat. And when the pressure gets big 267 00:14:44,040 --> 00:14:48,080 enough, the eruption begins, the fluids are evacuated, the 268 00:14:48,080 --> 00:14:50,520 eruption ends, and then the process repeats. 269 00:14:51,560 --> 00:14:54,480 But most geysers, many of them are quite irregular. 270 00:14:55,360 --> 00:14:59,120 There's only a very special subset that are truly periodic, 271 00:14:59,120 --> 00:15:02,240 or periodic means the interval between eruptions is always the 272 00:15:02,240 --> 00:15:05,360 same. And even for those that are 273 00:15:05,360 --> 00:15:09,960 periodic, that periodicity varies over time, over decadal 274 00:15:09,960 --> 00:15:12,680 time scales, or can be influenced by earthquakes or 275 00:15:12,680 --> 00:15:15,600 other processes. What about mud volcanoes? 276 00:15:16,200 --> 00:15:19,400 Mud volcanoes also erupt because the pressure in where the mud is 277 00:15:19,400 --> 00:15:23,520 coming from gets too high and so materials are ejected to the 278 00:15:23,520 --> 00:15:25,840 surface, right? So too much pressure underground 279 00:15:26,400 --> 00:15:30,000 mud volcanoes erupts sediment. So this means mud and rock 280 00:15:30,000 --> 00:15:33,240 fragments along with the mixture of water and gas. 281 00:15:33,880 --> 00:15:37,000 And often that gas is methane, natural gas, right? 282 00:15:37,000 --> 00:15:39,160 That methane is produced from the organic material that's 283 00:15:39,160 --> 00:15:42,120 buried with the sediment. And as it's heated to high 284 00:15:42,120 --> 00:15:44,760 enough temperature, that organic materials converted into 285 00:15:44,760 --> 00:15:47,320 methane. Mud volcanoes we often find in 286 00:15:47,320 --> 00:15:49,920 places where we also extract hydrocarbons from the earth, the 287 00:15:49,960 --> 00:15:53,320 oil and gas. And mud volcanoes can erupt this 288 00:15:53,320 --> 00:15:56,800 mixture of fluids, right, water, gas and sediment from as deep as 289 00:15:56,800 --> 00:15:59,720 10 kilometers. And they create land forms that 290 00:15:59,720 --> 00:16:01,880 resemble, in many ways, magmatic volcanoes. 291 00:16:01,880 --> 00:16:03,520 They can erupt sort of explosively. 292 00:16:03,520 --> 00:16:06,320 They can create mud flows. Yeah. 293 00:16:06,320 --> 00:16:08,760 Mud volcanoes can create mountains. 294 00:16:08,760 --> 00:16:11,080 They can create things that look like lava flows. 295 00:16:11,480 --> 00:16:14,560 In fact, I had the great pleasure of going to Azerbaijan, 296 00:16:15,280 --> 00:16:18,720 which is famous for many things, but for many people, the mud 297 00:16:18,720 --> 00:16:21,520 volcanoes are the big tourist attraction in Azerbaijan. 298 00:16:21,520 --> 00:16:24,600 There are fields and mud volcanoes on land as well as 299 00:16:24,600 --> 00:16:27,120 under the sea, under the Caspian Sea. 300 00:16:27,840 --> 00:16:32,240 And the source of the gas in the mud and the fluids are from the 301 00:16:32,280 --> 00:16:35,800 same sedimentary formations from which Azerbaijan is extracting 302 00:16:35,800 --> 00:16:39,480 the oil and gas. And if I was just looking at a 303 00:16:39,480 --> 00:16:43,240 satellite image of the morphology of the flows, I would 304 00:16:43,240 --> 00:16:46,120 not easily be able to tell, maybe not be able to tell at 305 00:16:46,120 --> 00:16:49,520 all, that those were made of mud and not lava. 306 00:16:50,520 --> 00:16:53,040 And they flow downhill. They make long flows. 307 00:16:53,040 --> 00:16:56,040 They look a lot like rhyolite flows, very silica rich flows. 308 00:16:56,960 --> 00:16:59,920 And they can also create spatter, fragmented mud that 309 00:16:59,920 --> 00:17:04,920 falls in the ground. And on Mars, there is debate 310 00:17:04,920 --> 00:17:08,400 about whether some of the landforms that people see little 311 00:17:08,400 --> 00:17:11,160 cones. Are they magmatic cones or are 312 00:17:11,160 --> 00:17:14,920 they produced by mud volcanoes? Presumably mud volcanoes don't 313 00:17:14,920 --> 00:17:18,280 last as long as magmatic wants. They must be very soft and 314 00:17:18,280 --> 00:17:21,960 easily kind of washed away. Yes, on a planet where there's 315 00:17:21,960 --> 00:17:25,720 precipitation, that precipitation will erode the 316 00:17:25,720 --> 00:17:27,680 sediment faster than it would erode lava. 317 00:17:28,680 --> 00:17:31,880 And I guess they're best preserved on land in very dry 318 00:17:31,880 --> 00:17:34,640 places, but also to under the ocean. 319 00:17:34,640 --> 00:17:37,840 A lot of the mud volcanoes on Earth form in submarine settings 320 00:17:38,040 --> 00:17:39,360 and they're they're better preserved. 321 00:17:40,160 --> 00:17:44,480 What happens when there are eruptions on the ice? 322 00:17:44,880 --> 00:17:47,480 Do you get the same amplifying effect? 323 00:17:47,480 --> 00:17:50,520 And can we see this kind of thing happening in Iceland? 324 00:17:50,920 --> 00:17:53,680 In ice is just the solidified form of water. 325 00:17:54,360 --> 00:17:57,000 So in the same way that Magma's, when they interact with water, 326 00:17:57,000 --> 00:18:01,600 can make steam and help Dr. explosive eruptions, the same 327 00:18:01,600 --> 00:18:04,320 process can happen when magma erupts under ice. 328 00:18:04,480 --> 00:18:08,760 But first, you have to melt the ice, and all that melt water 329 00:18:08,760 --> 00:18:12,600 that you're producing does help cool magma and help it solidify. 330 00:18:13,080 --> 00:18:17,440 And so lava flows that erupt under ice often cool fast enough 331 00:18:17,440 --> 00:18:19,320 that they don't erupt explosively. 332 00:18:19,880 --> 00:18:22,840 But there is a distinctive signature of lavas as they cool. 333 00:18:23,160 --> 00:18:25,920 When Magma's cool, they contract. 334 00:18:26,680 --> 00:18:29,080 And when they contract, they will make cracks to accommodate 335 00:18:29,080 --> 00:18:32,760 that change in volume. And maybe some of your listeners 336 00:18:32,760 --> 00:18:36,120 have been to Devil's Causeway in Northern Ireland. 337 00:18:36,480 --> 00:18:39,840 Here in California, there's a place called Devil's Post Pile, 338 00:18:40,400 --> 00:18:44,160 and these are sort of hexagonal vertical columns of lava. 339 00:18:44,600 --> 00:18:47,280 The columns are bounded by what we call cooling joints, the 340 00:18:47,280 --> 00:18:51,160 cracks made as the magma cools, and those cracks propagate 341 00:18:51,160 --> 00:18:53,120 perpendicular to the cooling front. 342 00:18:53,920 --> 00:18:57,720 And so if you cool a flat lava flow underwater, you get 343 00:18:57,720 --> 00:19:00,720 vertical cooling joints. If you're completely surrounded 344 00:19:00,720 --> 00:19:04,360 by ice, those cooling joints will be perpendicular to the ice 345 00:19:04,520 --> 00:19:08,320 lava contact, and so they'll often radiate A distinctive 346 00:19:08,320 --> 00:19:10,360 signature of lavas that cool under ice. 347 00:19:11,240 --> 00:19:15,360 In 2010, you may remember the Afioko eruption happened in 348 00:19:15,360 --> 00:19:19,000 Iceland and closed air traffic in northern Europe. 349 00:19:19,840 --> 00:19:22,560 That was probably the greatest disruption to air traffic in 350 00:19:22,560 --> 00:19:26,040 Europe since World War 2. And there the volcano erupted 351 00:19:26,040 --> 00:19:29,400 under ice, and that melt water flowed into the volcanic vent, 352 00:19:29,800 --> 00:19:32,280 helping to drive the exclusivity of that eruption. 353 00:19:32,440 --> 00:19:33,760 And that water had two effects, right? 354 00:19:33,760 --> 00:19:36,600 The water helped quench the magma to make the volcanic ash, 355 00:19:37,000 --> 00:19:40,120 and the steam generated from that cooling helped power the 356 00:19:40,120 --> 00:19:43,320 eruption. Let's talk about the second 357 00:19:43,520 --> 00:19:48,280 important way in which water effects an eruption, namely when 358 00:19:48,280 --> 00:19:53,760 water is already present in some form within the erupting magma. 359 00:19:54,760 --> 00:19:59,720 How does that amplify eruptions and where exactly does that 360 00:19:59,720 --> 00:20:01,800 water come from? So there are many parts to this 361 00:20:01,800 --> 00:20:03,360 question. Let's start maybe with where the 362 00:20:03,360 --> 00:20:07,520 water comes from and Magma's melted rock. 363 00:20:07,960 --> 00:20:11,240 And when you melt a rock, different elements in the 364 00:20:11,240 --> 00:20:14,080 periodic table either like to stay in the solid that's 365 00:20:14,080 --> 00:20:18,400 leftover or like to go into the melt that's produced. 366 00:20:19,080 --> 00:20:22,680 And water and lots of the other gases prefer to go into the 367 00:20:22,680 --> 00:20:25,120 melt. And so if you take a rock that 368 00:20:25,120 --> 00:20:29,480 has water in it and melt it, most of that water ends up going 369 00:20:29,480 --> 00:20:32,600 into the melt that's produced. And so where's that water coming 370 00:20:32,600 --> 00:20:34,480 from? There can be little bits of 371 00:20:34,480 --> 00:20:38,040 water trapped between crystals inside a rock in the what we 372 00:20:38,040 --> 00:20:40,640 call the pore space. But lots of minerals also 373 00:20:40,640 --> 00:20:43,320 incorporate water directly in the mineral structure. 374 00:20:43,640 --> 00:20:46,600 Clay minerals are an example. There's a mineral called 375 00:20:46,600 --> 00:20:49,080 amphibol that incorporates water in its structure. 376 00:20:49,320 --> 00:20:52,880 And so when you melt a rock that contains amphibol or rocks that 377 00:20:52,880 --> 00:20:56,240 contain clay, the water that was present ends up going into the 378 00:20:56,240 --> 00:20:58,840 melt. And that water that's in the 379 00:20:58,840 --> 00:21:02,640 melt that's formed is fundamentally important for why 380 00:21:02,640 --> 00:21:05,800 we have volcanoes at all. Volcanoes erupt because the melt 381 00:21:05,800 --> 00:21:08,240 that's produced is less dense than the surrounding crust. 382 00:21:08,600 --> 00:21:11,120 So for magma to erupt, we have to make it less dense. 383 00:21:11,520 --> 00:21:14,400 One way to make something less dense is to fill it full of gas, 384 00:21:14,960 --> 00:21:18,440 and at low pressure, the water that was dissolved in the magma 385 00:21:19,120 --> 00:21:20,880 is no longer able to be dissolved. 386 00:21:20,880 --> 00:21:24,160 It comes out of solution and forms bubbles, and it's the 387 00:21:24,160 --> 00:21:27,600 presence of those bubbles that helps Dr. Magma to the surface. 388 00:21:28,120 --> 00:21:32,280 So how do we get all this water into the interior of the earth 389 00:21:32,280 --> 00:21:35,560 in the first place? The process of plate tectonics, 390 00:21:35,560 --> 00:21:37,640 where we create plates at Earth's surface that move 391 00:21:37,640 --> 00:21:41,320 horizontally and then sink into the Earth through a process 392 00:21:41,320 --> 00:21:44,520 called subduction, is a great way to bring water from Earth's 393 00:21:44,520 --> 00:21:46,640 surface, from the oceans into the Earth. 394 00:21:47,440 --> 00:21:49,640 And that water is brought into the Earth through subduction in 395 00:21:49,640 --> 00:21:51,520 two ways. The sediments on top of the 396 00:21:51,520 --> 00:21:55,600 subducting plates, as they sink into the Earth carry with it the 397 00:21:55,600 --> 00:21:58,920 water between the betaments, and the minerals that contain water 398 00:21:58,920 --> 00:22:02,920 also gets abducted as well. And then at high pressure, those 399 00:22:02,920 --> 00:22:05,640 minerals can't hold that water, and they're released into the 400 00:22:05,640 --> 00:22:08,160 overlying part of the Earth we call the mantle. 401 00:22:08,800 --> 00:22:11,440 And that helps drive melting of the mantle. 402 00:22:12,160 --> 00:22:15,800 And when you melt wet rock, the water goes into the melt, it's 403 00:22:15,800 --> 00:22:19,120 carried upwards with that melt, and then powers the volcanic 404 00:22:19,120 --> 00:22:21,640 eruptions we see above subduction zones. 405 00:22:21,880 --> 00:22:24,600 I guess the other concept we should talk about is why is it 406 00:22:24,600 --> 00:22:28,760 that we make bubbles inside magma from that dissolved water? 407 00:22:30,160 --> 00:22:33,920 And the solubility of gases inside liquids increases with 408 00:22:33,920 --> 00:22:37,000 increasing pressure. And your listeners will know 409 00:22:37,000 --> 00:22:38,320 this from their everyday experience. 410 00:22:38,320 --> 00:22:41,600 When you open a carbonated beverage and you take off the 411 00:22:41,600 --> 00:22:46,440 top or you open the can, you decrease pressure and that 412 00:22:46,440 --> 00:22:49,040 carbonated beverage starts to fizz because you've lowered the 413 00:22:49,040 --> 00:22:50,240 pressure. And that's because the 414 00:22:50,240 --> 00:22:53,600 solubility of those gases is lower at low pressure. 415 00:22:53,800 --> 00:22:56,880 And so the water can't dissolve that carbon dioxide and it 416 00:22:56,880 --> 00:22:59,920 starts forming bubbles. And magma does the same thing at 417 00:22:59,920 --> 00:23:01,960 high pressure. It can dissolve a lot of water, 418 00:23:02,520 --> 00:23:05,280 but as the magma rises to shallower depths, the pressure 419 00:23:05,280 --> 00:23:08,000 decreases. The water was dissolved in the 420 00:23:08,000 --> 00:23:10,160 magma forms bubbles, and those bubbles grow. 421 00:23:10,920 --> 00:23:13,960 And if the magma keeps rising, the solubility of those gases 422 00:23:13,960 --> 00:23:16,440 keeps decreasing, and the gases expand. 423 00:23:17,160 --> 00:23:20,400 And it's that rapid expansion of the gas in the formation of 424 00:23:20,400 --> 00:23:23,840 bubbles that drives magma to the surface that makes volcanoes 425 00:23:23,840 --> 00:23:28,840 erupt and erupt explosively. So are we more likely to see wet 426 00:23:29,280 --> 00:23:32,480 magma or the effects of water and the bubbles that you just 427 00:23:32,480 --> 00:23:37,360 described in the tectonic settings where water has just 428 00:23:37,360 --> 00:23:40,840 been subducted, IE in subduction zones or above subduction zones? 429 00:23:41,240 --> 00:23:43,240 Yeah, exactly. Most of Earth's most explosive 430 00:23:43,240 --> 00:23:46,160 volcanic eruptions will happen in places where you can get a 431 00:23:46,160 --> 00:23:50,200 lot of water into magmas. And the best place to do that 432 00:23:50,200 --> 00:23:53,080 are subduction zones where you're bringing water down with 433 00:23:53,080 --> 00:23:56,640 the subductive plate that can enter into the source region for 434 00:23:56,640 --> 00:23:59,680 the magma and then gets carried back up to the surface. 435 00:24:00,080 --> 00:24:02,400 And so mid ocean ridges where plates are being formed. 436 00:24:02,400 --> 00:24:04,400 Those magmas tend to be relatively dry. 437 00:24:04,840 --> 00:24:06,800 At subduction zones, they tend to be quite wet. 438 00:24:07,760 --> 00:24:11,400 I'm not sure if this is related or a separate factor, but I know 439 00:24:11,400 --> 00:24:15,840 that the silica content of the melt is a critical determinant 440 00:24:16,040 --> 00:24:20,560 of viscosity, with the viscosity increasing quite dramatically as 441 00:24:20,600 --> 00:24:25,520 silica content increases. And so since high viscosity 442 00:24:25,520 --> 00:24:28,440 magma tends to block the conduits as it cools, it can 443 00:24:28,440 --> 00:24:32,000 lead to explosive eruptions when the pressure builds up and it 444 00:24:32,000 --> 00:24:35,760 kind of blows its top. Is this silica content 445 00:24:35,760 --> 00:24:40,520 variability independent of the volatile or water content of the 446 00:24:40,520 --> 00:24:42,520 magma? So maybe we should put the 447 00:24:42,520 --> 00:24:45,920 viscosity of magmas in perspective. 448 00:24:46,800 --> 00:24:50,880 The lowest silica content magmas we see, the types of rocks we 449 00:24:50,880 --> 00:24:54,680 call basalts, will have a viscosity or consistency very 450 00:24:54,680 --> 00:24:57,320 similar to something like syrup or honey. 451 00:24:58,280 --> 00:25:01,880 The more silica rich magmas like those we see in volcanic arcs 452 00:25:01,880 --> 00:25:05,640 have a viscosity similar to asphalt, so more than a million 453 00:25:05,640 --> 00:25:08,520 times greater. And the ability to flow is 454 00:25:08,760 --> 00:25:11,640 proportional to viscosity. And so that means the magmas and 455 00:25:11,640 --> 00:25:14,880 volcanic arcs will flow, you know, a million times more 456 00:25:14,880 --> 00:25:17,800 slowly given the same forces driving their motion. 457 00:25:18,680 --> 00:25:22,320 So the amount of silica in magmas has a huge effect on how 458 00:25:22,320 --> 00:25:25,200 they can erupt. So the question was whether 459 00:25:25,200 --> 00:25:27,760 there's a relationship between the amount of water and the 460 00:25:27,760 --> 00:25:31,640 amount of silica observation, if that's the case. 461 00:25:32,000 --> 00:25:35,000 And there's also a reason why. But I should point out actually 462 00:25:35,000 --> 00:25:38,520 that understanding how we make silica rich magmas is still the 463 00:25:38,520 --> 00:25:41,760 subject of quite active research, understanding what 464 00:25:41,760 --> 00:25:45,000 processes dominate and why. But there are two main ways in 465 00:25:45,000 --> 00:25:48,280 which we change the silica content of magmas. 1 is you can 466 00:25:48,280 --> 00:25:52,000 heat the surrounding rock and melt some of it and incorporate 467 00:25:52,000 --> 00:25:55,320 that into the magma sitting in the Crest, and we call that 468 00:25:55,320 --> 00:25:57,760 assimilation, where you incorporate the surrounding 469 00:25:57,760 --> 00:26:00,240 rock. The other process is that as 470 00:26:00,240 --> 00:26:02,920 magma sit in the Crest, they cool and they start to 471 00:26:02,920 --> 00:26:07,800 crystallize as they cool. And those crystals that form can 472 00:26:07,800 --> 00:26:10,880 settle out of the magma and be separated from the remaining 473 00:26:10,880 --> 00:26:13,200 liquid. And we call that fractional 474 00:26:13,200 --> 00:26:15,560 crystallization. Where we crystallize, we remove 475 00:26:15,560 --> 00:26:18,280 some of those crystals and it turns out the first crystals 476 00:26:18,280 --> 00:26:20,920 that form are relatively low in silica. 477 00:26:21,360 --> 00:26:24,200 So that means the magma that's leftover has more silica. 478 00:26:24,960 --> 00:26:28,440 And so through this combination of crystallizing and removing 479 00:26:28,440 --> 00:26:32,320 crystals and assimilating surrounding crust, over time the 480 00:26:32,320 --> 00:26:36,440 magma gets more silica rich. And earlier we talked about the 481 00:26:36,440 --> 00:26:39,720 importance of water liking to stand to melt. 482 00:26:40,640 --> 00:26:43,240 So in the process of melting the surrounding rock or 483 00:26:43,240 --> 00:26:47,160 crystallizing, whatever water was present gets concentrated in 484 00:26:47,160 --> 00:26:50,720 the melt that's leftover. So in the process of enriching 485 00:26:50,720 --> 00:26:53,600 magma and silica, you're also enriching it in water. 486 00:26:54,360 --> 00:26:56,320 And so the two tend to increase over time. 487 00:26:57,240 --> 00:27:00,960 Let's talk about how water is implicated in eruptions 488 00:27:01,040 --> 00:27:05,560 elsewhere in the solar system. Miles, for example, used to have 489 00:27:05,560 --> 00:27:09,880 lots of surface water and has some giant volcanoes. 490 00:27:10,560 --> 00:27:13,960 Can we see evidence of water affecting the volcanic activity 491 00:27:13,960 --> 00:27:16,280 there? Mars used to have abundant 492 00:27:16,280 --> 00:27:19,560 liquid water at surface, and there's still plenty of water on 493 00:27:19,560 --> 00:27:21,920 the surface today. We can see ground ice. 494 00:27:22,040 --> 00:27:24,840 The Phoenix Rover sort of exposed some of it when it dug 495 00:27:24,840 --> 00:27:27,640 into the ground. We can map some of the water 496 00:27:27,640 --> 00:27:31,160 with gamma rays with spacecraft, and they're big ice sheets at 497 00:27:31,160 --> 00:27:35,360 the North and South pole. I mentioned ice because there's 498 00:27:35,360 --> 00:27:38,160 a distinctive landform that's produced when lava flows flow 499 00:27:38,160 --> 00:27:42,320 over ice. We said that magma transfers 500 00:27:42,320 --> 00:27:44,840 heat to the surrounding environment, and if that's 501 00:27:44,840 --> 00:27:46,600 water, it can vaporize that water. 502 00:27:47,040 --> 00:27:50,120 When you flow over ice, you can melt some of that ice, and then 503 00:27:50,120 --> 00:27:52,680 you vaporize that ice. And so now you can imagine a 504 00:27:52,680 --> 00:27:56,320 lava flow flowing on top of ice. It's heating the underlying ice. 505 00:27:56,360 --> 00:27:59,840 That ice could be in the ground. The steam that's generated is 506 00:27:59,840 --> 00:28:03,200 buoyant and expanding, and it blasts its way through the lava 507 00:28:03,200 --> 00:28:05,680 flow, making a little tiny volcano. 508 00:28:06,280 --> 00:28:08,920 We can see fields of these little volcanoes on top of lava 509 00:28:08,920 --> 00:28:12,520 flows in Iceland, and people call them rootless cones, 510 00:28:12,760 --> 00:28:15,400 rootless because there's no actual magma deep underground. 511 00:28:15,400 --> 00:28:17,120 It's just a lava flow on which they're sitting. 512 00:28:17,880 --> 00:28:20,800 And people have mapped out these fields of rootless cones on 513 00:28:20,800 --> 00:28:24,640 Mars, so evidence that lavas flowed over frozen ground. 514 00:28:25,160 --> 00:28:27,640 The youngest volcanism on Mars happened in a place called 515 00:28:27,640 --> 00:28:31,640 Cerberus Fossae, just South of the Elysium volcano. 516 00:28:32,080 --> 00:28:34,680 And there's some long fissures we see on the surface of Mars. 517 00:28:35,000 --> 00:28:37,640 This is also where many of the recent Mars quakes have been 518 00:28:37,640 --> 00:28:39,600 detected from the Insight Lander. 519 00:28:39,600 --> 00:28:42,560 And it looks like there was recent explosive volcanism in 520 00:28:42,560 --> 00:28:46,480 that area that looks like it was generated by magma interacting 521 00:28:46,480 --> 00:28:50,000 with external water, either ice that it melted to incorporate 522 00:28:50,000 --> 00:28:52,960 water like we see in Iceland, or groundwater. 523 00:28:53,520 --> 00:28:57,280 What about some of the icy moons in the outer solar system, such 524 00:28:57,280 --> 00:29:01,000 as Saturn's moon and Solidus? You know, my lifetime, this was 525 00:29:01,040 --> 00:29:04,480 probably one of the most exciting observations from space 526 00:29:04,480 --> 00:29:07,920 exploration is detecting active eruptions on Enceladus. 527 00:29:08,480 --> 00:29:10,440 Enceladus is a small moon of Saturn. 528 00:29:10,880 --> 00:29:13,120 It's got a radius of 250 kilometers. 529 00:29:13,680 --> 00:29:16,520 It's covered with ice, and it's very cold out there. 530 00:29:17,240 --> 00:29:20,320 And so it's hard to imagine 4 1/2 billion years after the 531 00:29:20,320 --> 00:29:23,600 formation of our solar system, something as small as a little 532 00:29:23,680 --> 00:29:27,600 ice ball like Enceladus could be, have both liquid water and 533 00:29:27,600 --> 00:29:29,200 then be erupting that liquid water. 534 00:29:29,960 --> 00:29:33,720 But it is the Cassini spacecraft both imaged that plume and it 535 00:29:33,720 --> 00:29:36,240 flew through the plume and collected ice particles and 536 00:29:36,240 --> 00:29:38,400 measured the composition of those ice particles. 537 00:29:39,160 --> 00:29:42,320 And so now we understand that those eruptions are sourced from 538 00:29:42,320 --> 00:29:45,800 an ocean underneath the ice covered surface, probably a 539 00:29:45,800 --> 00:29:50,080 depth of say 10 kilometers. That ocean is a global ocean in 540 00:29:50,080 --> 00:29:53,600 contact with the rocky interior. We know that because the 541 00:29:53,600 --> 00:29:56,960 eruption is ejecting silica nanoparticles that come from 542 00:29:56,960 --> 00:29:59,560 that interaction with the rocky interior, and those are very 543 00:29:59,560 --> 00:30:02,520 powerful eruptions. They're sending ice particles 544 00:30:02,520 --> 00:30:04,800 into one of the rings of Saturn called the E ring. 545 00:30:05,760 --> 00:30:08,760 Not everything has escape velocity and leaves Enceladus, 546 00:30:08,760 --> 00:30:12,200 so a lot of the erupted material falls back on the surface as 547 00:30:12,200 --> 00:30:14,280 snow. And this actually makes 548 00:30:14,280 --> 00:30:17,200 Enceladus the most reflective object in her solar system from 549 00:30:17,200 --> 00:30:19,880 all that snow. And the eruptions on Enceladus 550 00:30:19,880 --> 00:30:22,280 are interesting. They're probably most like 551 00:30:22,280 --> 00:30:24,600 geysers. Geysers, we said, are boiling 552 00:30:24,600 --> 00:30:28,680 water and liquid water as rises through these cracks at the 553 00:30:28,680 --> 00:30:33,800 South polar region on Enceladus, as it gets to low pressure, that 554 00:30:33,800 --> 00:30:36,760 water also boils. And that volume expansion from 555 00:30:36,760 --> 00:30:38,400 boiling helps drive the eruption. 556 00:30:39,000 --> 00:30:41,960 And once everything enters into space, whatever liquid was there 557 00:30:41,960 --> 00:30:43,920 cools very quickly and forms ice particles. 558 00:30:44,760 --> 00:30:48,040 And the source of that heating to make it boil is tidal 559 00:30:48,040 --> 00:30:49,080 distortion. Yeah. 560 00:30:49,080 --> 00:30:52,480 The source of heating for the oceans in the outer solar 561 00:30:52,480 --> 00:30:56,680 system, ocean worlds is energy from tidal deformation. 562 00:30:57,200 --> 00:31:00,680 The orbits of these satellites around their host planet is not 563 00:31:00,680 --> 00:31:03,560 perfectly circular. And so when the satellite gets 564 00:31:03,560 --> 00:31:07,040 closer to the planet, gravitational attractions bigger 565 00:31:07,040 --> 00:31:10,160 and the planet deforms more. And then when it moves further 566 00:31:10,160 --> 00:31:13,880 away, deforms last, and that squishing and unsquishing the 567 00:31:13,880 --> 00:31:17,920 planet creates heat through friction, and that heat from 568 00:31:17,920 --> 00:31:21,320 friction warms the interior. And for some of these ocean 569 00:31:21,320 --> 00:31:24,360 worlds, that warming is enough to melt the ice to make a liquid 570 00:31:24,360 --> 00:31:27,200 ocean. Europa, which is one of the 571 00:31:27,200 --> 00:31:31,920 Galilean moons of Jupiter, is also covered in ice and it's 572 00:31:31,920 --> 00:31:36,280 crisscrossed with fractures. Do we see water erupting out of 573 00:31:36,280 --> 00:31:38,000 the ice there as well? Yeah. 574 00:31:38,000 --> 00:31:40,720 Whether there are eruptions analogous to those we see on 575 00:31:40,800 --> 00:31:46,200 Enceladus happening at Europa is uncertain, you might almost say 576 00:31:46,200 --> 00:31:49,120 controversial. The Hubble Space Telescope, for 577 00:31:49,120 --> 00:31:53,120 example, saw a plume of, or an anomaly of, of water vapour 578 00:31:53,120 --> 00:31:56,440 above the surface, but it's not detected all the time. 579 00:31:57,160 --> 00:32:02,280 So the question is, was it a false detection or contamination 580 00:32:02,280 --> 00:32:06,040 somehow of some signal? Or it could be the eruptions are 581 00:32:06,040 --> 00:32:10,080 episodic, and so they're on sometimes, not on other times. 582 00:32:11,160 --> 00:32:14,800 From the Galileo mission, it's not obvious that anything they 583 00:32:14,800 --> 00:32:17,120 saw could be attributed to active eruptions. 584 00:32:17,560 --> 00:32:20,040 But certainly when we look at the surface of Europa, we see 585 00:32:20,040 --> 00:32:23,600 features that are most easily explained, I think, by liquid 586 00:32:23,600 --> 00:32:26,880 water being either on the surface or very close to the 587 00:32:26,880 --> 00:32:29,280 surface. There's a type of terrain on 588 00:32:29,280 --> 00:32:32,960 Europa called chaotic terrain, where you see something that 589 00:32:32,960 --> 00:32:35,720 looks like a bunch of icebergs that have been displaced and 590 00:32:35,720 --> 00:32:39,720 rotated a little bit. And that requires mobility of 591 00:32:39,720 --> 00:32:42,920 those blocks of ice. And to enable mobility, it helps 592 00:32:42,920 --> 00:32:44,760 to have a liquid like liquid water. 593 00:32:45,920 --> 00:32:48,920 And we do know that Europa does have a liquid ocean underneath 594 00:32:48,920 --> 00:32:52,000 that ice covered surface. And it's a deep ocean. 595 00:32:52,000 --> 00:32:53,680 It's probably about 100 kilometers deep. 596 00:32:53,960 --> 00:32:57,240 And again, like instead of this tidal deformation heating it up 597 00:32:57,240 --> 00:33:00,560 and causing the water to seep up or blow through the cracks. 598 00:33:00,680 --> 00:33:02,400 Yeah, Jupiter has four big moons. 599 00:33:02,400 --> 00:33:07,640 The Galilean moons IO, Europa, Ganymede and Callisto and 600 00:33:07,640 --> 00:33:10,240 Callisto. Ganymede and Europa are probably 601 00:33:10,240 --> 00:33:12,880 all ocean worlds. What about IO then? 602 00:33:13,800 --> 00:33:17,760 We did an episode earlier. It's the most volcanic object in 603 00:33:17,760 --> 00:33:21,720 the solar system, but is there water involved there? 604 00:33:22,240 --> 00:33:26,800 So IO is the most volcanically active body in our solar system. 605 00:33:27,360 --> 00:33:32,600 And unlike its three neighbors, the ocean worlds covered in ice, 606 00:33:32,600 --> 00:33:37,200 it's closer to Jupiter. It's tidal deformation heating 607 00:33:37,200 --> 00:33:39,760 is much greater, and so it's much hotter. 608 00:33:39,840 --> 00:33:42,480 And it's so warm that all the water that would have been there 609 00:33:42,480 --> 00:33:46,080 has long since boiled away. But to make magmas erupt, you 610 00:33:46,080 --> 00:33:47,880 need something to lower the density. 611 00:33:48,040 --> 00:33:52,760 And so it could be that sulfur on IO plays the role that water 612 00:33:52,760 --> 00:33:57,160 plays with magmas on Earth. So it's the volatile component 613 00:33:57,160 --> 00:34:00,240 that starts forming gases and bubbles that helps drive the 614 00:34:00,240 --> 00:34:06,320 volcanic activity on IO. If you could decide where to 615 00:34:06,320 --> 00:34:10,440 send a new exploratory space mission to learn more about 616 00:34:10,440 --> 00:34:13,880 volcanism in the solar system, especially with regard to the 617 00:34:13,880 --> 00:34:16,760 effect of water, where would you choose? 618 00:34:17,320 --> 00:34:20,679 Enceladus, I think, is an easy choice in part because we can 619 00:34:20,679 --> 00:34:25,000 directly sample the ocean. The eruptions on Enceladus are 620 00:34:25,080 --> 00:34:28,520 delivering that ocean to us above the surface, making it 621 00:34:28,520 --> 00:34:30,280 easy to sample and easy to collect. 622 00:34:30,800 --> 00:34:32,639 And it's a very fresh sample as well. 623 00:34:33,760 --> 00:34:37,120 But I am always reminded that every time we visit a body we 624 00:34:37,120 --> 00:34:40,600 have not gone to before, there are great surprises. 625 00:34:40,840 --> 00:34:44,199 I never would have guessed, until New Horizons flew by Pluto 626 00:34:44,719 --> 00:34:47,199 that Pluto was such an interesting ocean world with 627 00:34:47,199 --> 00:34:51,320 such a rich geological history. I expected it would be a big 628 00:34:51,320 --> 00:34:53,280 ball of ice. And it's anything but. 629 00:34:53,880 --> 00:34:56,719 And I think the same is true for our exploration of Enceladus and 630 00:34:56,719 --> 00:34:59,080 the other moons in the Saturn system. 631 00:34:59,320 --> 00:35:01,320 They turn out to be quite a bit more interesting than we 632 00:35:01,480 --> 00:35:05,840 originally expected, in part maybe because their imagination 633 00:35:05,840 --> 00:35:09,040 is not good enough. Regardless, you know, every 634 00:35:09,040 --> 00:35:12,960 decade or so NASA commissions the National Academy of Sciences 635 00:35:12,960 --> 00:35:17,680 to undertake a decadal survey to identify the highest priority 636 00:35:17,960 --> 00:35:22,040 targets for space exploration. And the most recent NASA 637 00:35:22,040 --> 00:35:26,080 Planetary Science Decadal Survey recommended Uranus Orbiter to 638 00:35:26,080 --> 00:35:28,480 visit Uranus. And Uranus has a number of 639 00:35:28,480 --> 00:35:32,200 interesting moons, and that would be its highest priority 640 00:35:32,200 --> 00:35:35,640 flagship mission, followed by an Enceladus mission. 641 00:35:36,320 --> 00:35:39,280 And so Enceladus and its eruptions are clearly a 642 00:35:39,600 --> 00:35:42,520 community high priority for exploration. 643 00:35:43,600 --> 00:35:45,160 Of course, we have missions on the way. 644 00:35:45,400 --> 00:35:47,160 Let's see. The Dragonfly mission is heading 645 00:35:47,160 --> 00:35:49,840 to Titan. Whether Titan is an ocean world 646 00:35:49,840 --> 00:35:52,200 or not is the subject of some debate. 647 00:35:52,320 --> 00:35:55,400 I think until a year ago we all would have said Titan has an 648 00:35:55,400 --> 00:35:57,720 ocean. There's a paper published in 649 00:35:57,720 --> 00:36:02,800 Nature on December 17th, 2025, arguing in fact that Titan may 650 00:36:02,800 --> 00:36:05,400 not be an ocean world. But it would be an ocean of 651 00:36:05,440 --> 00:36:09,280 methane though. Titan has lakes and rivers and 652 00:36:09,280 --> 00:36:14,400 an atmospheric cycle where there is a liquid and that liquid 653 00:36:14,400 --> 00:36:17,720 would be hydrocarbons, methane, but that's in the very shallow 654 00:36:17,720 --> 00:36:20,480 part of Titan. As we go deeper below the 655 00:36:20,480 --> 00:36:25,480 surface, just like Enceladus or Europa, the interior is probably 656 00:36:25,480 --> 00:36:30,000 mostly water ice, and you get deep enough that water ice can 657 00:36:30,000 --> 00:36:34,080 melt to make a ocean of water. And we used to think Titan had 658 00:36:34,080 --> 00:36:37,400 an ocean. That may not be the case, but we 659 00:36:37,400 --> 00:36:40,920 do have other missions besides Dragonfly that has still to 660 00:36:40,920 --> 00:36:42,640 launch. We have Clipper on its way to 661 00:36:42,640 --> 00:36:47,400 study Europa. The Jupiter Icy Moons Explorer 662 00:36:47,520 --> 00:36:51,560 with the acronym JUICE is on its way to study 3 ocean worlds of 663 00:36:51,560 --> 00:36:54,440 Jupiter, right, Ganymede, Europa and Calista. 664 00:36:55,680 --> 00:36:58,920 So whether or not these new missions will come to fruition, 665 00:36:59,000 --> 00:37:00,840 we have a couple spacecraft on the way. 666 00:37:01,480 --> 00:37:03,000 What are you working on at the moment? 667 00:37:03,520 --> 00:37:06,480 In the last couple years I've had the great pleasure to go on 668 00:37:06,480 --> 00:37:09,680 a couple oceanographic expeditions to study submarine 669 00:37:09,680 --> 00:37:12,640 volcanism. The first was an International 670 00:37:12,640 --> 00:37:16,680 Ocean Discovery Program expedition to the Aegean, part 671 00:37:16,680 --> 00:37:19,840 of the Mediterranean, to study the volcanic history of 672 00:37:19,840 --> 00:37:24,480 Santorini volcano and the nearby Christiana and Colombo volcano, 673 00:37:24,640 --> 00:37:28,040 that whole volcanic field. And its goal was to understand 674 00:37:28,040 --> 00:37:30,840 the interaction between volcanism, tectonics, right the 675 00:37:30,840 --> 00:37:33,960 faulting and rifting to create those basins in which the 676 00:37:33,960 --> 00:37:36,920 volcano set and the evolution of climate. 677 00:37:36,920 --> 00:37:39,520 As sea level goes up and down, that change in pressure 678 00:37:39,520 --> 00:37:43,440 influences the volcanic system. And so in that setting, we can 679 00:37:43,440 --> 00:37:47,040 go all the way back 5 million years and look at the evolution 680 00:37:47,040 --> 00:37:49,920 of that system and sea levels going up and down. 681 00:37:49,920 --> 00:37:53,360 The faults are being activated and the volcanoes are erupting. 682 00:37:54,080 --> 00:37:57,120 And we can do that from the birth of the volcanic centers to 683 00:37:57,120 --> 00:37:59,480 their end in over multiple volcanic cycles. 684 00:37:59,920 --> 00:38:02,560 And so we drilled over 7 kilometers of holes and 685 00:38:02,560 --> 00:38:07,200 recovered thousands of meters of sediment to reconstruct that 686 00:38:07,200 --> 00:38:10,040 volcanic history and also understand the processes that 687 00:38:10,040 --> 00:38:13,120 drive submarine volcanism. And then in September of last 688 00:38:13,120 --> 00:38:16,840 year, I was on the Australian research Vessel investigator 689 00:38:16,840 --> 00:38:20,600 studying the Hunga eruption, recovering samples and mapping 690 00:38:21,000 --> 00:38:23,600 to understand what drove that eruption. 691 00:38:24,080 --> 00:38:28,360 And most of what erupted at Hunga powered that 57 kilometer 692 00:38:28,360 --> 00:38:31,440 high eruption. Most of what erupted collapsed 693 00:38:31,440 --> 00:38:35,200 and went underwater and was not transported in the atmosphere. 694 00:38:35,320 --> 00:38:38,440 And those underwater currents travelled very far and very fast 695 00:38:38,440 --> 00:38:41,720 underwater, snapping the communication cables that 696 00:38:41,720 --> 00:38:43,800 connected Tonga to the outside world. 697 00:38:44,880 --> 00:38:48,600 And so the expedition was aimed at trying to understand how the 698 00:38:48,600 --> 00:38:51,400 volcanic eruption collapsed and what happened to that material, 699 00:38:51,400 --> 00:38:54,520 what governed where it went and how it was transported. 700 00:38:55,160 --> 00:38:58,480 And did you see a caldera that? It was a big eruption, and so it 701 00:38:58,480 --> 00:39:00,800 left behind a hole in the ground. 702 00:39:01,720 --> 00:39:04,240 And one of the questions that motivated that expedition is 703 00:39:04,240 --> 00:39:07,600 understanding what that hole is. Was it a crater? 704 00:39:07,640 --> 00:39:10,040 And a crater is produced by just blowing stuff up. 705 00:39:10,360 --> 00:39:12,920 You can think about an impact. A meteorite hits the surface of 706 00:39:12,920 --> 00:39:17,160 the Earth and excavates a crater from the impact, as opposed to 707 00:39:17,160 --> 00:39:20,760 what we call a caldera, where the ground collapses because the 708 00:39:20,760 --> 00:39:24,840 magma underneath is evacuated and the overlying crust sinks 709 00:39:25,000 --> 00:39:27,720 into what used to be an area filled with magma. 710 00:39:28,520 --> 00:39:32,200 And we're still trying to figure out, do the images we see 711 00:39:32,200 --> 00:39:36,000 support the caldera or crater interpretation, But the 712 00:39:36,000 --> 00:39:39,200 diagnostic signature would be identifying the faults on which 713 00:39:39,200 --> 00:39:43,240 the ground would have collapsed. So hopefully as we continue to 714 00:39:43,240 --> 00:39:45,560 process all our data, we'll be able to resolve all these 715 00:39:45,560 --> 00:39:50,080 interesting open questions. Michael Mango, thank you very 716 00:39:50,080 --> 00:39:51,960 much. Thank you for the time today and 717 00:39:51,960 --> 00:39:53,960 for your listeners who joined for their interest. 718 00:39:53,960 --> 00:39:55,680 You know, volcanoes are really fascinating. 719 00:39:56,240 --> 00:39:59,560 That's a great life to be a volcanologist, and these are 720 00:39:59,560 --> 00:40:01,080 great times to be a volcanologist. 721 00:40:01,080 --> 00:40:02,840 And of course, there's so much still left to learn. 722 00:40:04,120 --> 00:40:06,800 To see pictures and illustrations that support this 723 00:40:06,800 --> 00:40:12,080 podcast, go to geologybytes.com, where you'll also find a subject 724 00:40:12,080 --> 00:40:14,000 matter index of all the episodes. 725 00:40:14,440 --> 00:40:17,800 There you can also give me feedback which I welcome, as 726 00:40:17,800 --> 00:40:20,800 well as sign up to get my emails about new episodes.