Explosions at Mount Saint Helens | How the Earth Was Made (S2, E10) | Full Episode | History

earth a unique planet restless and dynamic continents shift and clash volcanoes erupt  glaciers grow and recede titanic forces   that are constantly at work leaving a  trail of geological mysteries behind   this episode investigates the deadliest and  most destructive volcanic event in u.s history mount saint helens a pristine  snow-capped mountain suddenly blew   600 feet off her summit in a type of  eruption no one had ever witnessed before   scientists trying to understand what made this  event so lethal uncover evidence for one of the   biggest landslides in history a sideways-directed  blast that knocked over 230 square miles of forest   and mega mudflows that thundered down the  valleys and destroyed everything in their path what scientists have discovered from this unique   event brings geologists one step closer  to understanding how the earth was made in washington state 100 miles south of  seattle stands mount saint helens one of   20 major volcanoes that form part of the cascade  mountain range at the north american west coast   before may 18 1980 she was at the center of a  thriving recreational paradise and prosperous   timber industry the volcano had a beautiful  conical form it was called the mount fuji of   north america and the form was a bit concave  but beneath her beauty lay an ominous secret the mountain was brewing something  that had a deadly potential   the story began on march 20th 1980 when a 4.2  magnitude earthquake woke mount saint helens from   a slumber that had lasted 123 years the last known  eruption was witnessed in 1857 by local tribes in 1980 the earthquake was an alarming sign  because earthquakes may be an indication   that an eruption is building up earthquakes can  happen when magma rises from deep inside the earth   shifting and breaking the rock on its journey up  the very first signals we had were earthquakes   at shallow depth beneath the volcano and  within a matter of just a few days it was   clear this was something unusual so the word  went out to scientists around the country   and very quickly we started to converge at st  helens and started trying to understand what   was going on and what we saw was the volcano  was becoming more and more and more restless   volcanoes are dangerous because they are  hard to predict and in 1980 the science   of predicting volcanic eruptions was still  in its infancy the most recent explosive   eruption that occurred on the continental  usa was lawson peak in california in 1915.   since then most of the experience volcanologists  had gained came from studying quiet lava flows on   hawaii volcanoes are incredibly complicated  natural systems and they're always full of   surprises saint helen surprises us all the time  other volcanoes surprises but we're learning   armed with the latest scientific  equipment volcanologists were anxious   to study a possible eruption little did  they know that they were about to witness   the most deadly volcanic blast in the  u.s in living memory on coldwater ridge   six miles northeast of the volcano they installed  a trailer with highly sophisticated equipment   and began to closely monitor the mountain from  there they had a perfect view over the volcano we had a front row seat to seeing the evolution  and reawakening of a major cascade volcano   and we were fortunate in that we  had people here with a lot of energy   people were working 15 to 20 hours a day in addition to earthquakes another key indicator  for volcanic activity is gas emissions magma   made out of hot molten rock contains gases that  come from deep inside the earth 30 miles down   as magma moves up from these depths there is  less rock weighing down on it from above so the   pressure on the magma decreases gases dissolved  in the magma escape and rise to the surface   but gases are not just a telltale sign of  rising magma they are also responsible for   the explosiveness of the eruption the greater  the buildup of gas pressure within the volcano   the more explosive the eruption will be well  this is a simple experiment to demonstrate   the importance of gas pressure in a magma the  bottle is partially filled this is filled about   80 percent with water this will be simulating  a volcanic eruption so i'm going to carefully   place the bottle here we'll tilt it a little bit  away from me i'm going to put on my safety goggles   and now i'm about ready to start pumping here we  go oops there's a little bit of gas coming at the   bottom a little bit more and the pressures  are up to about 60 pounds per square inch   whoa did we get it we got it yeah like in the bottle the presence of gas at  the surface of a volcano is a sure sign that   an explosive eruption is building in spring 1980  cassataval's job was to detect these gas emissions   the gas he was looking for was sulfur dioxide   it's a gas that smells like rotten eggs  and is associated with volcanic activity   but the key to the measurements  wasn't the smell the secret   was subtle differences in the color of the light  this instrument looks at the light in the sky   and it looks for the presence of certain molecules  like sulfur dioxide which also absorb light from   the sky and it measures the difference between  the light absorbed by sulfur dioxide and the light   available in the rest of the sky in march  and april 1980 cassataval and his team were   using this instrument to detect the amount of  escaping gases they assumed that the gas levels   would increase prior to the eruption as more  and more magma would rise inside the volcano but in 1980 the assumption proved wrong  gas emissions didn't change even though   earthquakes were getting stronger and hundreds  of small tremors were recorded there was really   no significant variation it was a very low level  of sulfur dioxide emissions and there was nothing   in those emission rates that really indicated  that an eruption was was just around the corner   but by late april after five weeks  of tremors the mountain gave them   another clue to what was brewing inside on the  north face a huge bulge was growing outwards   a casual observer would look at the  volcano and say well it's no longer a nice   fuji type shape but in fact the north side now  is bulged out and it was obviously deformed   in some way and we were trying to understand  what could have been causing that deformation   it was the first time scientists were able to  monitor the deformation of a mountain on coldwater   ridge they installed an instrument that uses laser  technology to get precise measurements as to how   fast the bulge was growing what we were trying to  do was to focus a laser beam from this instrument   on a reflector in the volcano receive the return  reflected signal and then measure that distance   the reflectors they used were small mirrors about  three inches across they had fixed on the bulge as   was the case in 1980 before may 18th the north  flank of the volcano was moving outward it was   bulging outward and so the distance was getting  shorter and what we learned is that from cold   water too that distance was getting shorter about  five feet a day by may 11th the bulge had expanded   outward a staggering 450 feet jurisan had a hunch  that it was caused by rising magma of course as   volcanologists you always want to know what's  going on under the earth's surface and that's the   great challenge because you can never go there you  can only observe from the surface we knew that the   north flank was deforming we knew that something  had to be causing it to deform what could that be   well it could be magma forcing its way up into  the volcano shoving the north line aside that was   a possibility well what else could be causing it  well maybe the earthquakes were simply causing the   volcano to become unstable as a result of gravity  maybe there was just a slow landslide going on   it was very difficult to understand or to make  a measurement that would tell you the difference   the plausible story was that magma was  forcing its way up under the volcano   as the bulge grew the flank of the mountain became  increasingly unstable still scientists had no idea   how deadly the eruption would turn out to be so  we didn't know for sure until until it happened   but as the bulge continued to grow we knew we were   getting closer to the final outcome  we just didn't know what that would be there were other signs that  an eruption was imminent   earthquakes became more frequent and  stronger as time went on authorities   feared the worst and zoned off the area around  the volcano with limited access for the public in spring 1980 geologists were dealing with  a number of clues that mount saint helens   was building to an eruption earthquakes were  an indication that the volcano was waking up despite low and unchanging gas emissions a growing  bulge on the north face suggested that the magma   was indeed on the rise mysteriously after may  14th the volcano quieted down there was hardly any   seismic activity and the bulge grew at a slower  rate on may 17th officials gave in to pressure   and allowed some people with property inside the  restricted area to gather up whatever they could   another group was scheduled to enter for 10 am  the next morning but on that day disaster struck on the morning of may 18th scientists were   about to witness one of the worst  volcanic disasters in modern history for more than two months a team of volcanologists  had been monitoring mount st helens   it's another reason why 18 was a surprise because  basically all of this data we collected before   there wasn't anything that that told that  you know may 18th was going to be the day   david johnston a young volcanologist with the  u.s geological survey was on duty that day he   had spent the night on coldwater ridge to  carry out measurements of the growing bulge   it's interesting that even on the morning of may  18th the measurements that dave made indicated   that it that bulge was still growing at about the  same rate the same morning dan miller was on his   way to coldwater ridge to check on the time-lapse  camera they used for filming the north face   i was headed to the north on interstate five out  of vancouver washington and as i got a few miles   north of town there's a overlooked point as you  go down the highway where you can look off to   the east and see mount st helens and i looked  over there and it was a beautiful clear day   and there was mount st helens with this giant  mushroom cloud going up above it at that point   i knew something very serious was underway from  a safe distance 35 miles away miller witnessed   how the eruption unfolded the first thing i did  was went to our radio our communications radio   and i made some calls up to dave to try to  raise him and find out what was happening   and not only did i not reach dave but even our  repeater which was on a mountain peak that was a   another few miles to the north of coldwater 2 did  not answer indicating that it had been destroyed   and that was very scary at that point i realized  that something bad had probably happened to dave   thick dark smoke was billowing out  of the crater obscuring the view   within hours daylight turned murky gray and  reduced visibility up to 300 miles northeast it wasn't until 24 hours later that the air  was clear enough for scientists to inspect the   devastation the entire landscape was almost  unrecognizable to those of us who had spent   almost two months before the big explosion on  may 18 working up there every day suddenly i   realized that there was complete and utter silence  there were no insects there were no small animals   and there were no colors the only color was ash  gray for as far as i could see we made our way   up along the edge of the ridge and we found  the small quarry where dave's trailer and our   vehicle had been parked on the morning of  may 18th and we could see that it was gone   it was it was a ferocious place coldwater 2  was on the 18th and nobody had a chance there   neither johnston nor the trailer were ever found  a total of 57 people were killed along with   thousands of deer elk bears and other wildlife  230 square miles of forests were destroyed and   the eruption had torn a 2 000 foot wide crater in  the summit it was no longer a beautiful fuji type   volcano and in fact we could see that the top of  the volcano appeared to be missing or was obscured in the months to come scientists faced the  difficult task of finding out what exactly   happened on that fateful day they searched  the ground for clues and methodically pieced   together the chain of events that had led to  the devastation the first important clue was an   earthquake measuring 5.2 that shook mount saint  helens at 8 32 that morning the second piece of   evidence came from photographs taken by tourists  who flew over the mountain around the same time   they looked down and they were able to document my  series of photographs some shaking on the top of   the mountain and then right afterwards the whole  front of that mountain started to move sideways   in a series of still photographs they  documented how the bulge collapsed   a magnitude 5.1 earthquake caused the north flank  which was greatly weakened by the deformation to   break loose in the form of a giant landslide  the volcano just couldn't take it anymore   and the north flank became unstable and slid away within seconds hundred feet of the mountain  slid down and destroyed everything in its path what used to be a quiet mountain valley  with the toodle river running through it   was now filled with debris up to 600 feet high  forming a hilly terrain known as the hummocks from the amount of debris from the landslide  scientists calculated that two-thirds of a   cubic mile of rock slid down the mountain enough  to bury washington dc under 50 feet of rubble   it was one of the biggest landslides ever  recorded in history it tore a gaping hole   in the side of the mountain almost two  miles wide and over two thousand feet deep to scientists it was a mystery why suddenly the  entire northern flank of the volcano collapsed   geologists today can still  follow the trail of destruction what we're looking at here is a part of a large  debris avalanche we're looking at one of the   hummocks and this is a rock outcrop that's  actually outcropping in the hummocks and the   coloration that you see first of all is telling  you that this has been altered this color provides   an important clue to why the landslide became so  big instead of the usual black volcanic lava rock   it is yellow this is a sign that the rock  came in touch with hot water turning some   of the minerals in the rock yellow geologists  found the same yellow rock in the crater wall   suggesting the discoloration must have happened  on the mountain before the eruption so you have   rain water or glacial water that seeps down into  the mountain gets close to the magma heats back   up and as it comes out of the mountain then it  starts to change and chemically alter these rocks   and turning them you know into these different  colors but the hot water didn't just change the   color more importantly it also weakened the rock  so you can see how crumbly these rocks are just by   kind of digging your hammer through here and the  reason they're so crumbly is because when the hot   water moves through and alters them they sometimes  alter to clay in some really soft materials so if   you took any other rock it would be much stronger  this yellow crumbly rock isn't just found here   but stretches over 17 miles throughout the valley  suggesting that large parts of the mountain were   rotten weakened before the eruption so probably  what had been happening over thousands of years is   magma down on the volcano heating up water and  this with this this acidic water was gradually   rotting out the center of the volcano it  couldn't be seen anywhere at the surface   when the bulge on the north side finally collapsed  it pulled along big parts of the rotten volcano   and left behind the horseshoe-shaped  crater st helens is famous for today this volcano is just a sand pile if you  will it had very little internal integrity   or strength so that when failure did occur  literally part of the mountain slid away   but more destruction was to come within minutes  of the landslide mount saint helens channeled   her fury into another deadly force the air turned  absolutely black so i don't know if you could see   anything but a few of these witnesses that managed  to survive out in the very edge the ground shook   intensely and they sensed that all the trees were  coming down at once even though they couldn't   see it the landslide had spread east and west  but this force surged in a northerly direction   within three or four minutes it destroyed  everything on coldwater ridge and ripped out   trees in a 230 square mile fan-shaped area so  even where we're sitting here eight miles from   the volcano you can see this ridge behind  me this ridge is three thousand feet tall   and all the texture that you see on this ridge  are the trees the old growth forest trees that   were blown down by the surge that went up and over  this thing like it wasn't even there and so for   the surge to have gone up and over this it had to  have still been going roughly 300 miles per hour   and then it continued nine miles further than  that before it finally stopped to geologists   this was a surprise they had never witnessed  a sideways eruption before well most of us had   gone to school studying the idea that volcanoes  erupt directly up they erupt into the atmosphere   and they they go vertically and i think most of  us were thinking that that was probably the style   of eruption we were going to see here at st helens  eventually because that's how volcanoes erupt   scientists were intrigued as to what had caused  this devastating surge so they began searching   the ground for evidence five miles northeast of  the crater wait is revisiting the old deposits mixed with burned wood from the shredded trees  he also finds rock to the untrained eye there   is nothing unusual about it but not so for the  experts it's clearly young rock it's relatively   light and um there's lots of little voids in here  in other words little bubbles that are frozen in   the rocks so this was the rock that was growing  there's a hot hot liquid almost solid liquid that   was growing inside mountain allens and causing  the bulge before may 18th this small rock was   a crucial piece of evidence for scientists  trying to figure out the chain of events after the landslide tore a gaping  hole into the north flank of the   mountain it exposed the magma underneath  without a cap of earth to keep it sealed   the magma suddenly expanded and surged outwards  pulling along rock from inside the mountain   you can envision it as sort of a colossal-sized  ash hurricane it was a cloud of rocks   and ash and hot gases that was maybe several  thousand feet thick that was moving across the   countryside at speeds of several hundred miles  an hour very turbulent mixture with blocks as   large as three or four feet in diameter flying  through the air it was incredibly destructive after the initial surge mount  saint helens turned quiet for half an hour there was calm and tranquility  then the volcano began hurling its fury skywards an enormous mushroom cloud formed high above  the volcano three times as tall as mount everest   ferocious explosions went on for hours releasing   huge amounts of energy equal to 27  000 hiroshima sized atomic bombs what happened on may 18 1980 became  a landmark event for scientists   it provided them with an unprecedented chance  to study a lateral eruption discolored rock in   the valley and in the crater wall where evidence  that the mountain was rotten before the eruption gray volcanic rock nine miles north of the  volcano was evidence that the landslide uncorked   a massive lateral blast at 5 30 in the evening  the volcano began to slow down until it finally   quit but there was more impending danger as the  eruption had caused another cataclysmic effect on may 18 1980 mount saint helens exploded  in a type of eruption never witnessed before one of the largest landslides  in history triggered a powerful   sideways-directed blast ferocious explosions  followed and formed an immense mushroom cloud late that afternoon the volcano slowed  but more chaos was about to strike   as the eruption had triggered  another destructive process   hot volcanic ash had melted the snow fields on  top of mount saint helens hundreds of tons of   milk water mixed with soil and formed a series  of mud flows that cascaded down the slopes most people don't realize that this hazard can  affect people living so far downstream because   up to 100 miles from a volcano is can still  be a hazard zone for these kind of volcanic   mudflows the biggest of the mud flows came down  the toodle river valley on its way there it   reached record speeds of 90 miles per hour and  raced over hills as high as 20-story buildings   it destroyed a total of 27 bridges nearly 200  homes and more than 185 miles of highway and roads today its remains are still preserved  on the banks of the tudol river   this deposit is an excellent example  of what we scientists call a lahar but   other people refer to as a mudflow big massive  flow of material that's much like wet concrete   that was coming down the river as a huge wall of  material pushing logs and debris in front of it   at first it was a mystery how this mud flow  had become so big but the rocks provided a clue   what we see are rocks of different type that  have come down from mount st helens some of   these are actually from the original cone of the  volcano that collapsed as the debris avalanche   geologists could now piece together  what caused these destructive mud flows   these rocks from high up in the  volcano came from the landslide   that had been thrown in the valley  in the first minutes of the eruption   when melt water mixed with the landslide debris  it formed a gigantic mudflow this incredible   torrent lasted till late that night and dumped  more than 65 cubic miles of mud along the way   even 30 years later proof of its destructive power  is still in the field these lahars came down and   totally buried this forest we see these standing  stumps of trees that are the remains of what   is often referred to as a ghost forest this was  buried by this lahar the trees were killed and   we only see them now because of the erosion  of the river which has come back in and eroded   into the bank and uncovered them so this  is a fantastic clue of you know the the   power and the destruction of this lahar which  which completely inundated this lower valley but one deposit further upstream was  causing confusion in the investigation   it looked like a lahar deposit but instead of  volcanic rock it was full of rounded river pebbles   the scientist who first studied this wasn't  sure this was a lahar deposit because it   contained so much of this rounded river rock  which is characteristic of stream bed deposits   and not lahars but then he realized that it  had this very very hard compact matrix in it   and it was not bedded or layered in any way and  came to the conclusion this had to be a huge lahar   that was probably something on the order of the  flow of the amazon river scientists were stumped   not only did this deposit have  rounded river rock it was also much   bigger than the deposit from the mud flow  that tore through the valley on may 18th if it wasn't part of the 1980  lahar where did it come from   geologists decided to investigate further and took  samples back to the lab radiocarbon dating showed   that this deposit swept down the valley three  thousand years ago if we had been standing on   this spot about three thousand years ago we would  have first heard a very low rumble that would have   gotten louder and louder and if we hadn't heated  that warning we would have seen a huge wall of   broken trees and debris coming around the river  bend probably at 30 or 40 miles an hour that would   have been hundreds of feet high and that wall of  debris and mud and rock would have then just swept   through here like a huge freight train literally  wiping the valley clean of anything in its path but where did this ancient monster flood  come from the only place that could have   stored that amount of water and rounded  rock was spirit lake 35 miles upstream   this discovery was crucial because there was an  impending danger that nature would repeat itself   not only did the landslide that initiated the  1980 eruption flow west into the toodle valley   it also went east into spirit lake and blocked  its exit as rivers and melt water kept flowing   in water rose to dangerous levels it became a very  big wake-up call for the hazards community because   if this sort of flood in lahar had happened in the  past it could happen again and the 1980 deposit   damned spirit lake once again with the same type  of weak unstable dam that had existed in the past   authorities had to act quickly within a couple of  years spirit lake would have filled up again and   had it been allowed to over top it would have  caused a catastrophic flood just like the one   3000 years ago the corps of engineers came in they  immediately devised a plan which involved pumping   water out of the lake to keep the lake level  stable for the short term their long-term solution   was to drill a a boring through a mountain ridge  creating a permanent drain so that spirit lake   could never get above that height and the danger  for an overtopping flood was then eliminated   scientists now understood  what happened on may 18th volcanic rock in mud deposits along the banks of  the toodle river valley is evidence that gigantic   mudflows thundered down mount saint helens and  rounded river pebbles in a 3 000 year old mud   deposit became a warning sign that spirit lake was  able to spill over and cause an even bigger lahar   in the summer of 1980 scientists thought the may  eruption was their chance of a lifetime because   major volcanic eruptions in the cascades happen  only once or twice every hundred years but they   were soon to be proven wrong after two decades  of inactivity the mountain began to stir again the explosion of mount st helens in may 1980  scarred the mountain with a massive crater on its   north side but in the summer after the eruption  the volcano began to rebuild itself thick magma   slowly rose to the surface and formed a dome  inside the crater had the activities continued   at the same rate it would have taken about 200  years to rebuild the mountain to its pre-1980 size but in 1986 magmaflows ceased  and the volcano died down   life returned to normal and adapted to  the new landscape plants and trees took   hold in the fertile volcanic soil elk and  other animals migrated back to the mountain then on september 23 2004 the ominous rumbling  began again and put volcanologists on alert the   entire cascade range in the western us produces  on average about two eruptions every century   so you think well that's one eruption per  career and saint helens in 1980s was ours and we   all assumed that that was it but we got a  second chance mount saint helens was cooking up   another mystery small earthquakes became stronger  and more frequent gps measurements detected that   the area around the mountain was sinking there  was one continuously recording gps instrument   around the volcano and its code name was jr01  jr01 had not moved in any unusual way right up   until the day the earthquake started and then on  that very day it started to move it moved toward   the volcano and downward as if that entire area  of the crust was sagging down toward the volcano the only plausible explanation for the  sinking land was that the magma reservoir   deep underground was shrinking in earlier surveys  scientists had detected a vast pool of molten rock   eight miles under the volcano if it was  getting smaller magma had to be on its way   up towards the throat of the volcano the renewed  activities caused widespread concern scientists   feared another eruption was building up and they  were puzzled what kind of eruption it would be   in search of an answer scientists turned to  saint helen's early days volcanoes are all   very individual they have individual types of  eruptions and traits and what they've done in   the past is what they're going to do in the future  the key to past eruptions is ancient volcanic rock   mike clint has specialized in mapping these old  deposits southwest of st helens he investigates   an area covered with large dark boulders a close  look reveals the type of eruption they formed in   we know that this rock came from a lava flow  because it has big crystals set in a much   finer grain ground mass of little crystals the  big crystals grew in the magma chamber while   the magma was deep under the volcano and the  fine-grained ground mass which is tiny crystals   grew when the lava erupted at the surface and  froze radiocarbon dating established the rock   was born 2500 years ago the nature of the eruption  it formed in was slow and quiet this kind of lava   flow erupts from the mountain as a liquid and it  flows down the mountainside under gravity as it   flows away from the mountain it cools until it  becomes so viscous that it can't flow anymore   so that's where it stops and that's what you  see here is the end result of emplacement of   this kind of lava flow so they're not dangerous  you can stand and watch it come down at you from deposits like these scientists could tell  that mount saint helens had produced a number   of quiet lava outpourings in the last 300 000  years they slowly built up the mountain from   a small cluster of rock to a conical shaped  volcano but northeast of the mountain clin   finds a different deposit which tells a story of a  much more dangerous episode in saint helen's past   we look at this deposit and there's a  couple of characteristics that are important   first of all that it's very loose and that it's  composed of rock fragments that are all about the   same size another important characteristic is that  the rock fragments are touching each other there's   no material in between them well that tells us  that these rock fragments came here by falling   out of the air it's a big explosive eruption  that sends the material very high into the sky   and when the wind dies down they  start to fall and they pile up here   the rock fragments are very light pumice  that form during a violent eruption   similar to the one that produced  the huge mushroom cloud in may 1980   but age dating revealed that  this deposit was much older this event happened 3500 years ago and compared  to the 1980 eruption scientists found evidence   that it was much more dangerous and spewed out  four times more rock and ash this is the biggest   eruption in mount st helen's history and it was  about a cubic mile of material that was erupted   at this time and we know that because we trace  out the deposit measure its thickness and its   distance you add that all up together and you  get the volume of the eruption this deposit can   be traced all the way to central canada studying  mount st helen's past has revealed that she has an   unpredictable eruptive nature well saint helens  had everything from relatively benign lava flows   to quite violent eruptions in the past so it's  very hard when a volcano starts acting up to know   which of these possibilities is going to happen  and of course the various scientists we discuss   and argue and all that kind of stuff what we think  is going on and nobody truly knows what's going on   scientists investigating mount saint  helens have found clues that show   different eruptive behaviors in her past large  dark boulders are evidence that she is able to   produce slow and quiet eruptions a thick  deposit of white pumice is evidence for an   ancient dangerous eruption four  times larger than the one in 1980 fortunately the events that began in 2004 took a  lucky turn the magma did reach the surface but it   had lost its explosive power it flowed out like  toothpaste in a dome-building style of eruption   as geologists carried on studying mount saint  helens a volcano 4000 miles away began to stir   because of their experience in  1980 scientists were convinced   a major catastrophe was about to unfold  and this time 12 000 lives were at risk the eruption of mount st helens in may 1980 took  scientists by surprise it was the first time   they witnessed the failure of a massive bulge  a huge landslide and a powerful lateral blast prior to 1980 we just we just didn't have  the knowledge to make those kinds of specific   predictions we started learning in the 1980s at  st helens we've continued to learn at volcanoes   around the world and we've we've had some  successes forecasting volcanic eruptions is   difficult because there is no strict pattern to  the buildup but as scientists are getting more   experienced in observing volcanic behavior  they are getting better at their predictions in 1995 suffriere hills volcano on the  caribbean island of montserrat became   restless it had been quiet for 350 years  until earthquakes rumbled it to life again residents were used to a gently steaming  mountain and simply hoped it would die down but when the earthquakes got  stronger officials called for help   a team of u.s volcanologists flew to  the caribbean to monitor the reawakening   there developed a situation there where whereby  there was a region of high seismicity occurred   just the saint helens if you went up on the  mountain as we did they just about knocked   it to your knees they were very strong events  strong earthquakes weren't the only warning   signs on the south side of the mountain they  observed how a monstrous bulge began to form   there were cracks that were occurring you could  see the cracks were moving every day it looked   like the whole side could fall apart so we could  get a slope collapse there a major slope collapse   by october 1997 the bulge was growing at a  staggering rate of 280 cubic feet per second   scientists were alarmed because  of their experience on mount st   helens they knew that a collapse  of the bulge was imminent   people living in the proximities of the volcano  were in danger so they advised the authorities   to evacuate immediately we did recognize we had  a situation analogous to saint helens we could   get the debris avalanche we could get a lateral  blast there were people in this instance that   were living there and they ought to get the heck  out eight thousand people had to leave the island   over four thousand were forced to  move to a safer location to the north   on the 26th of december 1997 the  volcano struck after an intense swarm   of earthquakes a huge part of the bulge  broke loose and roared down the valley like at mount saint helens the sudden  removal of rock released the pressure   on the magma below a lateral blast surged south  and spawned a vertical ash column 36 000 feet   high within 15 minutes the eruption destroyed  four square miles of the island and completely   buried the island's capital plymouth under 39  feet of mud it wasn't just damaged severely   it was eradicated it was a bulldozer that was  carried off into the sea and dumped into the sea   as a result of this so the lateral force was  just tremendous monserrat is a prime example   where lessons learned from a big catastrophe  have prevented another one almost everything   that i created saint helens did a credit monster  it replicated saint helens not only in the lateral   blasts and so forth but it did everything  that saint helens did on a smaller scale   scientists studying the eruption of mount saint  helens on may 18 1980 have uncovered a sequence   of events they had never seen before a  growing bulge on the north flank of the   mountain was an alarming sign that a pool  of magma was building up within the volcano   gray volcanic rock from the bulge five miles away  was evidence for a powerful sideways eruption   a 3 000 year old mud deposit became a warning sign  that the valleys around the mountain have been   repeatedly swamped by huge mudflows a deposit of  white pumice rock found all the way up to canada   showed that mount saint helens is able to produce  eruptions four times larger than the one in 1980   as the investigation has shown mount saint helens  is full of surprises st helens i think of it as a   teenager among the cascade volcanoes it's it's  young it's vigorously active it's explosive   it's very energetic even though to our eye as  we look at it it appears to be sleeping it's   it's active it's doing what it's been  doing for tens of thousands of years   mount st helens looks set to continue her  erratic and at times violent outbursts   her deadly potential is a stark  reminder the earth is never at rest you

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Id: 4HIc6nBzsVg

Length: 45min 12sec (2712 seconds)

Published: Sat Dec 12 2020