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read it highly recomended great book

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the David A Johnston guy in the green box

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mt saint helens 1857

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mt shasta

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this is mt shasta

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so sad

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The impact of Mt St.Helens

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op gif mount saint helens is super cooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooool

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what if mount saint helens did not erupt

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A car in Portland got covered in ash from the eruption

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this is the top view of mount St Helens. I wonder if any other volcanos erupted like this.

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Here is a diagram about what happened to mount St. Helens.

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Here is a video of the magma inside

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This is what happened after Mount St.Helens erupted.

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Can you believe this picture of St. Helens is made by ai? it looks like a real picture 😮

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This is another video of the eruption of Mt. St. Helens from britanica.com

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Volcanic eruption of Mount Saint Helens in Washington | Britannica

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On May 18, 1980, as geologists watched in awe, Mount Saint Helens erupted with tremendous force.

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Satellite photo of Mt.Saint.Helens after the eruption.

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This is a picture of Mt. St Helens's eruption and landslide

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Here is a picture taken of Mt. St. Helens explosion🤯

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Do you think that Mt saint helens will erupt again?

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At 8:32 a.m. PDT on May 18, 1980, Mount St. Helens, a volcanic peak in southwestern Washington, suffers a massive eruption, killing 57 people and devastating some 210 square miles of wilderness.

Called Louwala-Clough, or "the Smoking Mountain," by Native Americans, Mount St. Helens is located in the Cascade Range and stood 9,680 feet before its eruption. The volcano has erupted periodically during the last 4,500 years, and the last active period was between 1831 and 1857. On March 20, 1980, noticeable volcanic activity began with a series of earth tremors centered on the ground just beneath the north flank of the mountain. These earthquakes escalated, and on March 27 a minor eruption occurred, and Mount St. Helens began emitting steam and ash through its crater and vents.

Small eruptions continued daily, and in April people familiar with the mountain noticed changes to the structure of its north face. A scientific study confirmed that a bulge more than a mile in diameter was moving upward and outward over the high north slope by as much as six feet per day. The bulge was caused by an intrusion of magma below the surface, and authorities began evacuating hundreds of people from the sparsely settled area near the mountain. A few people refused to leave.

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At 8:32 a.m. PDT on May 18, 1980, Mount St. Helens, a volcanic peak in southwestern Washington, suffers a massive eru...

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Before and after look at the land to and how different it is.

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A quick check up of mount st. Helens!

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Could there be volcanos hidden in debris that haven't been active in a while?

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Can there be other volcanos like Mt. St. Helens?

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This is a picture of Mt. St. Helen's tiny plume smoking

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when do you think MT ST HELENS will erupt

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when do you think MT ST HELENS will erupt

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Eruptions can really cause a lot of dammage(Mt. St. Hellens😳🤯). First comes the the tectonic plates to shift and clash, then the earthquakes, after there is the bulge on the volcano, and finnaly the eruption causing the dammage.

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This is a photo of Mt. St. Helens before and after the eruptions.

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How do you know a volcano is about to erupt with only a few high magnitude level earthquakes?

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Pick one!

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Do you think Mount Saint Helens will erupt?

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Of course not like what are you thinking?

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????? how?

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how long will it take Mt.St. Helens to erupt again? 

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I think after that other eruption in the 1860's caused the May 18th 1980 one

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I think after that other eruption in the 1860's caused the May 18th 1980 one

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When did Mt. St. Helens form as a mountain?

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When did Mt. St. Helens form as a mountain?

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MT ST HELLEN BLOWING IT'S TOP! CRAZY!!!!!!

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I hope everyone answers this including Ms. Harrington. is there a more destructive volcano in the USA that is not in Hawaii?

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You show Declan a graph or diagram of it

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HELICOFTER LANDING ON MOUNT SAINT HELENS RIGHT AFTER THE ERUPTION

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AI generated photo of mt.saint helens

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This is the hybrid view of mt.saint helens

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I wonder.... how much debt or money that the people that lived there had to pay for the damage

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I wonder.... how much debt or money that the people that lived there had to pay for the damage

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I wonder how much the people that lived there had to pay after the eruption! probably more than 1 million dollars

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destroyed house from Mt.st Helens eruption

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Before May 18, 1980, this is what Mt St. Helens looks like.

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this is the part it destroyed

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Official websites use .gov
A.gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock () or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Publications

John W. Ewert, Angela K. Diefenbach, David W. Ramsey

Volcano Hazards Program, Volcano Science Center, Agrigan, Ahyi Seamount, Alamagan, Anatahan, Asuncion, Belknap, Black Butte Crater Lava Field, Black Rock Desert Volcanic Field, Blue Lake Crater, Carrizozo Lava Flow, Cascade Range Weekly Update, Cinnamon Butte, Clear Lake Volcanic Field, Coso Volcanic Field, Crater Lake, Craters of the Moon Volcanic Field, Daikoku Seamount , Davis Lake Volcanic Field, Devils Garden Lava Field, Diamond Craters Volcanic Field, Dotsero Volcanic Center, East Diamante, Esmeralda Bank, Farallon de Pajaros, Fukujin Seamount , Glacier Peak, Guguan, Haleakalā, Hell's Half Acre Lava Field, Hualālai, Indian Heaven Volcanic Field, Jordan Craters Volcanic Field, Kama'ehuakanaloa, Kasuga 2, Kīlauea, Lassen Volcanic Center, Long Valley Caldera, Mammoth Mountain, Markagunt Plateau Volcanic Field, Maug Islands, Mauna Kea, Mauna Loa, Medicine Lake, Mono Lake Volcanic Field, Mono-Inyo Craters, Mount Adams, Mount Bachelor, Mount Baker, Mount Hood, Mount Jefferson, Mount Rainier, Mount Shasta, Mount St. Helens, Newberry, Ofu-Olosega, Pagan, Red Hill-Quemado Volcanic Field, Ruby, Salton Buttes, San Francisco Volcanic Field, Sand Mountain Volcanic Field, Sarigan, Soda Lakes, South Sarigan Seamount, Supply Reef, Ta'u Island, Three Sisters, Tutuila Island, Ubehebe Craters, Uinkaret Volcanic Field, Valles Caldera, Wapi Lava Field, Weekly Update, West Crater Volcanic Field, Yellowstone, Zealandia Bank, Zuni-Bandera Volcanic Field

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Official websites use .gov A.gov website belongs to an official government organization in the United States. Secure .gov websites use HTTPS A lock () or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites. Publications John W. Ewert, Angela K. Diefenbach, David W.

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I wonder how Mt. St. Helens will explode next? Will it be outward, upwards, or it just won't explode?

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top of mt st hellens!

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These are some scientists flying over .

Mt.Saint Helens

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Flying Over Mount St. Helens: 1980 Volcanic Eruption Explained

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Ariel view of Mt . Saint Helens

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Does anyone know the exact amount of rock blown off the sides of Mt.St.Helens?

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Parts of the cloud from Mt. St. Helens went all the way around the world!

I bet you didn't know that.

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sunset at Mt.Saint Helens

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Aanika

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Do you think Mount St . Helens will erupt again in the future ?

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This is the uses map with plate boundaries-Namya

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Usgs tsunami picture with plate boundaries – Namya

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I wonder if Mt.St.Helens is related to Mt.Shasta.

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Do you think Mt.St.Helens is still active

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Video of Mt.St.Helens

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This is a 3d USGS map of Mt.Saint.Helens

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This is a USGS map of Mt.St.Helens

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Mt. St. Helens eruption

-Ayaan

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maybe every mountain is a volcano and we don't know it

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What is this animal and why is it doing a handstand? (Hint: the black and white colors might give you a clue.)

Voting for this episode is now closed. Would you like to vote on the most recent poll?

I pulled three questions from my jar. Which question do you want to explore next week?

How do elevators work?

-Maisey, 3rd Grade

What's the most dangerous animal in the ocean?

-Kimaya, 5th Grade

Why do we get headaches?

-Jaxon, 4th Grade

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Watch the video to discover the answer to "Could a mountain turn into a volcano?" and don't forget to vote for next week's question!

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how high did the explosion go?-Ian

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This is a diagram of Mt saint Helen’s.

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Distribution of ash from Mt. St. Helens eruption

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Distribution of ash from Mt. St. Helens eruption

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Drones Sacrificed for Spectacular Volcano Video | National Geographic

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Best Video of Mount St Helens Volcano Eruption

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Photographing a Catastrophic Explosion at Mt. St. Helens

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The most important photographs turned video of Mt. St. Helen's explosion was taken by an amateur photographer, and helped geologists determine the strength and power of the explosion (From Discovery Channel's "Raging Nature")

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See the most recent activity at Mount St. Helens!!!

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See the most recent activity at Mount St. Helens!!!

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Seismicity

Short-cut to Spectrograms for Mount St. Helens

Seismicity at Mount St. Helens is quite variable depending on the volcano's eruptive state. Most earthquakes are located at a shallow depth directly under the volcano; however there is a St. Helens Seismic Zone (SHZ) that extends north and south of the volcano on which some earthquakes take place. Seismicity changes character just before eruptions begin. There is usually an increase in both number and size of earthquakes as well as a change in the character of the seismograms. Such changes were detected and recognized as precursors to most of the two dozen or so eruptions during the past 30+ years including a two month precursory sequence before the cataclysmic eruption of May 18, 1980. On average (not during eruptions or their precursors) we locate about 17 earthquakes a month at Mount St. Helens. Most of these events are in the depth range of -2 to +2km. During eruptions and eruption precursor periods earthquakes are even shallower. There have been a few times during the past thirty years that there have been many earthquakes in the depth range 1-5 km. We interpret these events to be in response to stresses generated by magma recharge into the main crustal magma system. Such recharge seems to have taken place during the periods: 1989-1991, late in 1995 in 1997 and perhaps a few periods since the end of the last eruption such as mid 2014 and 2016.

NOTE: A depth of 0.0 (zero) km is at sea level and thus events within the volcano will plot above sea level (negative depths). See the blog for more details.

Recent Seismicity (2016 - present)

Here is a time-depth plot of earthquakes located directly under Mount St. Helens since 2016. This plot is updated weekly ... unless, of course unusual activity takes place that suggests a different time sequence is needed to better interpret that activity. Keep in mind that the PNSN earthquake recording and processing system changed in very major ways starting in 2012 and thus there can be small biases or changes introduced in event detection, location and size. We think these changes are small but one should still be aware of this possibility.

Here is a seismicity plot that shows the number of located earthquakes per day (black spikes) and the cumulative number of earthquakes over time (red). This can point out periods when more earthquakes were located. However, sometimes this is because more effort is taken to locate very small events such as at least partially is the case during the summer of 2014 when the iMUSH experiment was being installed in the region around Mount St. Helens.

Here is a map of the last year's epicenters at Mount St. Helens color coded by depth and with symbol size proportional to magnitude. Most events are shallow and lie within the crater.

Note: Black circles represent events about sea level (negative depths).

Past Seismicity (1980 - 2020)

Below you will find time-depth and seismicity plots for Mount St. Helens shown by decade, most recent first progressing back in time. These show the typical or background levels of earthquakes under the volcano as well as the intense activity associated with eruptions and magma recharge. We do not include epicenter maps here because at the normal scale produced they don't show anything of interest. Virtually all earthquakes locate directly under the volcano with concentrations under the crater, similar to the epicenter plot for recent events shown above. Much of the variability in these locations is due to inaccuracies in determining the exact locations. Of much more interest is the depth progression of earthquakes and their distribution in size and depth with time.

Since the spring of 1980 there have been a sufficient number of seismograph stations located on (8) or very near (11) the volcano such that the regional seismic network can reliably detect and locate earthquakes of magnitude 0.0 and larger in this area. Even smaller earthquakes can sometimes be detected and located though many also are missed.

Time-depth and seismicity counts for 2010 - 2020

During the decade of 2010 - 2020 there was no volcanic activity at Mount St. Helens; however there were several periods of increased seismic activity, particularly in the depth range from 0 - 5 km below sealevel. We think that these slightly higher levels of earthquake activity represent periods of slight pressure increases due to the replinishment of magma into the crustal resevoir below the volcano. There were similar and more intense sequences back in the 1990s.

Time-depth and Seismicity for 2000 - 2010

From Sep. 2004 to Jan. 2008 the volcano was in mild, continuous dome-building eruption (green bar shows eruption time) and produced over a million earthquakes, far more than could be located using traditional methods. A sub-sample of events was analyzed and located and is shown in the following figures. After the eruption quit (Jan. 2008) the seismicity decreased to normal background levels and since then all detected events have been analyzed and are shown in these figures.

Time-depth and Seismicity for 1990 - 2000

There were no eruptions of Mount St. Helens during this decade, however, there were periods during which seismicity in the depth range of 0 to 6 km depth is interpreted as due to magma recharge into a crustal magma zone. Such recharge may be relatively continuous with periods of increased flow or pressure or it may be truely episodic. Periods during which we interpret recharge to be taking place are marked with orange bars on the time-depth plot.

Time-depth and Seismicity for 1980 -1990

The summary plots for the 1980s can not show all the detail of what went on during this period but as an overview, note the following things:

1) Lots of large shallow earthquakes in the spring of 1980 leading up to the major eruption on May 18

2) Each subsequent eruption had some sort of shallow precursor (earthquakes or volcanic tremor) in the hours to days before they started

3) Deep (2-15+ km) and mostly small earthquakes followed the major explosive eruptions of May 18 and May 25

4) Deep and very small earthquakes took place around the time of the late-winter, 1982 eruption that we now think represented a new batch of gas charged magma arriving in the crustal magma zone

5) Again, deep seismicity starting in 1989 and continuing off and on through the 1990s that we interpret as due to pressure increases due to magma recharge.

The orange bars on the time-depth plot represent approximate periods where we think magma recharge is taking place. Green arrows (and a bar) on the seismicity plot represents times of eruptive activity, of which only the first few events had a major explosive component.

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Mount St. Helens | Pacific Northwest Seismic Network

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The PNSN is the authoritative seismic network for Washington and Oregon state.

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Mt saint Helen’s destruction video

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Revisit the riveting news coverage as Mount St. Helens erupted

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This links to Mount St. Helens' Facebook and Instagram page, which I will be showing in class a little. Facebook and Instagram are not allowed for your age, but your parents may be willing to show you these pages from their own Facebook and Instagram accounts.

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The volcano has its "first eruption in over 100 years." Steam explosions blasted a 200- 250 ft wide crater through the volcano's summit ice cap and covered the snow-clad southeast sector with dark ash.

March 27 to April 22, 1980
Eruptions occurred on average from about 1 per hour in March to about 1 per day by April 22 when the first period of activity ceased.

Small eruptions resumed on May 7 and continued to May 17. By that time, more than 10,000 earthquakes had shaken the volcano and the north flank had grown outward about 450 ft to form a prominent bulge.

earthquake occurred causing a "massive landslide" on the northern side, followed by a lateral blast. The debris avalanche swept around and up ridges to the north, but most of it turned westward traveling as far as 14 miles down the valley of the North Fork Toutle River. The landslide removed part of the cryptodome (a very hot and highly pressurized body of magma), triggering powerful eruptions that blasted laterally through the sliding debris. As the lateral blast of hot material overtook the debris avalanche; it accelerated to at least 300 mi per hr. Within a few minutes an eruption cloud of blast tephra began to rise from the former summit crater, quickly reaching 15 miles high.

12:15 pm - Beginning just after noon, the volcano entered the "Plinian phase" which continued for the next 9 hours producing a high eruption column, numerous pyroclastic flows, and ash fall downwind of the eruption. The pyroclastic flows reached speeds of 50 to 80 mi/hr and spread as far as 5 miles to the north. Scientists estimate that the eruption reached its peak between 3:00 and 5:00 p.m.

Over the course of the day, winds blew 520 million tons of ash eastward across the United States. Complete darkness occurred in Spokane, WA almost 250 miles from the volcano. Major ash falls occurred as far away as central Montana and in the Great Plains of the Central United States, more than 930 miles away. The ash cloud spread across the U.S. in three days and circled the Earth in 15 days.

May 25, June 12, July 22, Aug 7, Oct 16-18, 1980
The volcano has "smaller explosive episodes," each of which produced eruption columns 8-9 miles above sea level and pyroclastic flows down the volcano's north flank.

Beginning in October 1980, episodic eruptions built a new lava dome that reached nearly 1000 ft above the crater floor. Minor explosive activity, and sometimes lahars (a mixture of water and volcanic debris that moves rapidly downstream), accompanied several of the 1981 to 1986 episodes. In addition to the 17 dome-building episodes, hundreds of small explosions of gas and steam occurred, sending ash a few hundred feet to several miles above the volcano.

Between August 1989 and October 1991, at least six small ash-producing explosions occurred from the Mount St. Helens dome complex. Several of the explosions were accompanied by avalanches of snow and rock, pyroclastic density flows, ballistic projectiles, and debris flows.

Sources: USGS Volcano Hazards Program: 1980 Cataclysmic Eruption and USGS Scientific Investigations Report 2017-5022-C

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Library Guides: 40 Years Later: The Eruption of Mt. St. Helens and the USGS Response: Overview

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Library Guides: 40 Years Later: The Eruption of Mt. St. Helens and the USGS Response: Overview

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The TNM Download Client is built on modern web technologies and features a simplified approach to downloading products from The National Map.

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Please watch this video of someone climbing mt st helens .-Aaliya

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What someone found on Mt. St. Helens 37 years after the eruption

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What someone found on Mt. St. Helens 37 years after the eruption

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What I found on Mt. St. Helens 37 years after the eruption

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Footage of the 1980 Mount St. Helens Eruption

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Footage of the 1980 Mount St. Helens Eruption

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Footage of the 1980 Mount St. Helens Eruption

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Mt. St. Helen’s on a topographic map

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Click on the map to display elevation.

About this map

> United States > Washington > Skamania County > Mount Saint Helens

Minimum elevation: 5,052 ft

Maximum elevation: 8,310 ft

The Mount St. Helens major eruption of May 18, 1980 remains the deadliest and most economically destructive volcanic event in U.S. history. Fifty-seven people were killed; 200 homes, 47 bridges, 15 miles (24 km) of railways, and 185 miles (298 km) of highway were destroyed. A massive debris avalanche, triggered by a magnitude 5.1 earthquake, caused a lateral eruption that reduced the elevation of the mountain's summit from 9,677 ft (2,950 m) to 8,363 ft (2,549 m), leaving a 1 mile (1.6 km) wide horseshoe-shaped crater. The debris avalanche was 0.6 cubic miles (2.5 km3) in volume. The 1980 eruption disrupted terrestrial ecosystems near the volcano. By contrast, aquatic ecosystems in the area greatly benefited from the amounts of ash, allowing life to multiply rapidly. Six years after the eruption, most lakes in the area had returned to their normal state.

Wikipedia ( CC-BY-SA 3.0)

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Click on a map to view its topography, its elevation and its terrain.

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Mount Saint Helens topographic map, elevation, terrain

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Visualization and sharing of free topographic maps. Mount Saint Helens, Skamania County, Washington, United States.

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Why did the magma creep up the mountain in the first place?

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Why did the magma creep up the mountain in the first place?

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This is the picture of Mount St Helen’s before the eruption, after the eruption and how it is right now/current.

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Do you agree with me? Write it down in the comments.

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When will Mt saint Helen’s erupt again ????

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Video of Mt saint Helen’s.

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Mount St. Helens Eruption 18.05.1980 Part 2

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This is a video of Mt saint Helen’s erupting!!!!!!!

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Footage of the 1980 Mount St. Helens Eruption

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Why did the south part of the mountain erupt but not the north side

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Why did the south part of the mountain erupt but not the north side? 

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I think I know it but I also don’t think I know it

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This is the after picture when it erupted.

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I wonder why their was so much smoke but no lava even though it is kind of a volcano?

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I wonder why the eruption happened sideways? -Olivia s.

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I wonder if mount ST. Helens will erupted on the other side.

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How does water make an volcano restless?

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How does water make an volcano restless?

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Before and After Maps of Mount St. Helens

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Before and After Maps of Mount St. Helens

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MOUNT St. HELENS ERUPTION, May 18, 1980

May 17, 1980, before the eruption. (Courtesy USGS, photo by Harry Glicken)
Click here or on image for view of Mt. St. Helens after the eruption.

Mount St. Helens, located in southwest Washington State, is a typical stratovolcano. The volcano is one of several that line-up to form the Cascade Range, which extends from northern-central California northward into the Province of British Columbia in Canada. Six of the volcanoes are shown below in relationship to the convergent plate boundary separating the Juan de Fuca and North American plates.

2.1 Approximately how far is Mount St. Helens from the convergent plate boundary separating the Juan de Fuca and North American plates?

Mount St. Helens, like the other volcanoes of the Cascades, is composed of andesitic and rhyolitic pyroclastic materials. Some of the pyroclastic material has been remobilized as landslides and lahars. As explained at the beginning of this lab exercise, eruptions of stratovolcanoes can be catastrophically explosive. In May, 1980, Mount St. Helens did just that. The images at the top of this page show the state of the mountain before and after the May, 1980 eruption.

Let's take a closer look at the relationship between andesitic/rhyolitic volcanism and a convergent plate boundary. Below you can examine a larger scale map of the area, and an east-west cross-section (A-A') from the plate boundary to Mount St. Helens. For the purpose of comparison, the scale is the same as the scale used on the map and cross-section of the Island of Hawaii.

Stratovolcanoes are typically circular in plan, about the size of the circle shown on map. The radius of Mount St. Helens is about 6 km at the base, and the elevation of the base is about 1 km above sea level. Before the eruption of May, 1980, the elevation at the top of Mount St. Helens was about 3 km.

2.2 Using this information, and modeling the stratovolcano as a simple cone-shape, estimate the volume of volcanic material in Mount St. Helens, in cubic kilometers (km³). To remind you, the volume of a cone is given by the following formula,

volume = (1/3)*pi*r²*h,
where pi ~ 3.14, r = radius of the cone, and h = height of the cone.
2.3 How does this compare with the volume of a shield volcano, as exemplified by the Island of Hawaii?

The cross-section (above the map) shows the relationship between the convergent plate boundary and the volcanism. In the case of Mount St. Helens, like the other stratovolcanoes of the Cascades, the production of the andesitic/rhyolitic magma is ultimately related to the subduction of the Juan de Fuca plate beneath the western edge of the North American plate. Oceanic crust of the Juan de Fuca plate and sedimentary material (light green) are being shoved downward, toward the east, underneath North America. This down-going material undergoes metamorphism as it becomes exposed to progressively higher pressures and temperatures in the interior of the earth beneath North America. Earthquakes generated near the top surface of the down-going Juan de Fuca plate originate at a depth of about 75 km beneath Mount St. Helens. That's about where the top of the Juan de Fuca plate is located directly beneath Mount St. Helens. Temperatures at these depths can be as high as 1200 C, hot enough to cause some partial melting of the metamorphosed basalt of the subducting oceanic crust. The metamorphism also releases volatile (gas) components such as H ₂O, CO ₂, and SO ₂. The relatively small amounts of basaltic magma and rather large amounts of volatile gasses migrate upward, ultimately encountering the base of the overlying continental crust. Here, the basaltic magma and volatile gasses contribute to partial melting of the base of the continental crust. The magma thus formed is andesitic and rhyolitic, reflecting the composition of the lower part of the continental crust. Generally, only very small amounts of the basaltic magma ever reach the surface. The greater part of the basaltic magma becomes mixed, sort of homogenized, with the andesitic/rhyolitic magma. This andesitic/rhyolitic magma readily dissolves, quite literally soaks up, the volatile components. Under the very high pressures at such depths near the base of the continental crust these dissolved gasses are effectively trapped in the magma. However, the buoyant, gas-charged magma tends to work it's way upward toward the surface (intrusion). Most of the andesitic/rhyolitic magma cools and crystallizes before it ever reaches the surface, forming sometimes vast plutonic (intrusive) bodies of granodiorite/granite. Only comparitively small amounts of the gas-charged andesitic/rhyolotic magma ever reach the surface, but when this happens - LOOK OUT! The rapid formation of gas bubbles in the magma and their explosive expansion can have catastrophic effects. See the "before eruption" and "after eruption" images of Mount St. Helens, at the top of this page.

2.4 How might these "vast plutonic bodies of granodiorite and granite" ever become exposed at the surface? (Hint: Rock Cycle)

Now, let's take a closer look at the physiography (shape) of a stratovolcano. In the case of Mount St. Helens, this makes for an interesting "before" and "after" study of the effects of a eruption. Below, you can examine "before" and "after" topographic maps of Mount St. Helens.

Before the May 18, 1980 eruption, Mount St. Helens was a simple cone-shaped stratovolcano, typical of very many stratovocanoes around the world. The elevation at the top was 9677 ft (~3000 m). Oops, I apologize here for getting away from the metric system in these maps and some you will see later. The unit of measure is "feet" in all of the existing maps from which these were constructed. For what you will have to do, this won't make any difference. So you will be doing your work in "feet."

The slope of the flanks of a stratovolcano are pretty much controlled by the angle of repose of the coarser pyroclastic material making up the greater part of the volcano.

2.5 What is the slope and angle of the slope of the surface of Mount St. Helens along the red bar in the "before" map above? The length of the red bar is 10,000 ft.

2.6 How does this compare with the slope and angle of slope of flanks of a shield volcano?

One way to examine the effects of the eruption is to construct "before" and "after" topographic profiles of the volcano. The diagram below shows how this is done for a topographic profile along the segment X-X' (marked on the maps above) for Mount St. Helens before the May 18, 1980 eruption.

Basically, the topographic profile shows how the elevation changes along a specified line on the map, here X-X'. It's just a graph of elevation (vertical axis) versus horizontal distance (horizontal axis). It should come as no surprise to you that this just makes a side-view of the mountain. O.K., so now you know what Mount St. Helens looked like before the eruption, when viewed from the east. Wouldn't you like to know what Mount St. Helens looked like just after the eruption, from exactly the same vantage point?

2.7 Well, get to work. Construct the post-eruption profile on the hand-out of the map shown above. The pre-eruption profile is shown for comparison.

2.8 On your copy of the post-eruption profile, mark the following regions, (1) where there has been no change, (2) where material has been removed, and (3) where material has been added (deposited).

2.9 As nearly as you can estimate, what is the thickness of pyroclastic material (mostly ash) that has been deposited at the spot marked X'? The best way to do this is to estimate the elevation at X' on the "before" and "after" maps, then subtract.

The amount of material that was removed from Mount St. Helens has been estimated at 6.5 km ³ (cubic km). Most of this material was old volcanic material that was part of the volcano before the eruption. Some of this pulverized pyroclastic material was carried aloft and to the east by the wind, where it settled on the ground in noticeable amounts as far away as Montana. In Idaha, some 500 km east of Mount St. Helens, volcanic ash blanketed the landscape in a layer up to 5 mm thick.

2.10 The amount of material (6.5 km³) that was removed from Mount St. Helens represents what percentage of the original volcano? (Help: You need your answer to item 2.2.)

There is another way to examine some of these changes, by superimposing the "before" and "after" topographic maps. Take a look.

In these superimposed topographic maps you can identify basically three kinds of regions, (1) where the contour lines superimpose nearly exactly, (2) where the contour lines don't coincide and the "after" elevations are higher than the "before" elevations, and (3) where the contour lines don't coincide and the "after" elevations" are lower than the "before" elevations.

2.11 What does it mean if the "after" elevations are higher than the "before" elevations?
(HINT: no change, material added, material removed.)

2.12 What does it mean if the "after" elevations are lower than the "before" elevations?
(HINT: no change, material added, material removed.)

2.13 On your copy of this map, shade in the three regions. If you have color pencils or markers, use the following scheme for shading in the different regions. Regions of type 1, "no difference," leave blank. Regions of type 2, green. Regions of type 3, red.

Based on this kind of analysis, it becomes obvious that the explosion of the Mount St. Helens and dispersal of pyroclastic material was not the same in all directions.

2.14 In what direction was the explosion directed? What is your reasoning?

NOW YOU HAVE COMPLETED THE SECOND PART OF THE LAB EXERCISE.

PROCEED TO THE NEXT SECTION ON THE SOUFRIERE HILLS, MONTSERRAT
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MOUNT St. HELENS ERUPTION, May 18, 1980 May 17, 1980, before the eruption. (Courtesy USGS, photo by Harry Glicken) Click here or on image for view of Mt. St. Helens after the eruption. Mount St. Helens, located in southwest Washington State, is a typical stratovolcano.

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I wonder why it erupted so suddenly. -Olivia s.

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I wonder why it erupted so suddenly. -Olivia s.