It has been more than a hundred years since Mount St.
Helens last erupted, but the mountain is still an active volcano and it has been giving off steam for the past 5 years.
Mount St.
Helens, the deadliest volcanic eruption in the history of the United States.
Miles beneath Mount St.
Helens, instruments have caught something on the move.
It has triggered hundreds of earthquakes, the biggest surge since its last eruption ended.
The last time this volcano woke up, it gave two months of warning, then blew out its entire side and killed 57 people.
Nestled in the rugged beauty of the Pacific Northwest, Mount St.
Helens has long been a symbol of both tranquility and hidden power.
But this time, the mountain is [music] breaking the rules.
It is shaking and it is sinking.
So, what is moving down there?
And why won’t the ground rise?
Stay to the end and you will know the single measurement that separates a quiet year from the beginning of the end.
The signal under the mountain.
Here is what those instruments have been picking up.
Deep under the mountain, the ground is moving.
Not enough for you to feel.
You could stand directly over it holding a cup of coffee and the surface of your coffee would not so much as tremble, but it is enough for the instruments.
It started building around 2023 and it came into sharp focus across the first half of 2024.
By the early 20th century, Mount St.
Helens was affectionately known as the Mount Fuji of America.
It snowcapped peak drawing adventurers and nature lovers from far and wide.
Between early February and the middle of June that year, the network of seismometers wrapped around Mount St.
Helens logged close to 350 small earthquakes.
For a volcano that had spent years mostly still, that was a jump that got attention.
It was the largest short-term rise in earthquake activity the mountain had shown since its last eruption wound down in 2008.
That surge has since faded.
But here is what you need to understand from the start.
The earthquakes were only the symptom.
The thing that was actually moving down there, the process that set them off, did not stop when the headlines did.
By every sign scientists have, it is still underway beneath the mountain right now.
And this is not just any mountain.
This is the volcano that 46 years ago taught an entire country what a volcano can actually do.
Its gray cloud turned day into night in towns hundreds of miles away.
So when the earthquake count rises under Mount St.
Helens, it is never just a number on a chart.
It is a question.
And people downstream in the river valleys that drain this mountain have every reason to want the answer.
If you want to see exactly what that answer is and the one sign scientists are waiting for, subscribe now because this story isn’t finished.
The paradox.
Now look closer because this is where the story bends.
When a volcano is getting ready to erupt, it usually tells you in two ways at once.
My first impression in other words was one of not [music] quite chaos but certainly uh an unmanaged situation where where we were just reacting to what the volcano was doing rather than than knowing exactly what was going on.
The ground shakes because rock is cracking as magma forces its way upward.
And the ground swells because all that rising material has [music] to go somewhere and the surface bulges outward the way a balloon does when you blow into it, shaking and swelling.
Those two signals tend to travel together.
At Mount St.
Helens, only one of those signals showed up.
While the ground under the mountain has been shaking, the ground on top of the mountain has not been doing what the frightening version requires.
[music] It has not been swelling.
It has not been bulging outward or lifting upward.
If [music] anything, the surface has been doing the opposite, and it has been doing it for years.
The mountain is slowly, measurably settling, sinking.
Put those two facts side by side, and you can feel the problem.
[music] The earthquakes say energy.
The shape says the air is going out of the tire, not into it.
Those two things are not supposed to happen together.
And the whole story of this mountain right now lives in the gap between them.
[music] So, which is it?
Is Mount St.
Helen’s winding down or is it reloading?
What is actually moving?
Scientists have a name for what is happening down there.
They call it recharge.
It is a small dry word.
And if you are not careful, you will read right past what it actually describes.
Picture a tank buried far beneath the mountain.
A tank that fills very slowly from below.
Not a dramatic gush, but a trickle of molten rock rising over months and years, collecting in a chamber, pressing outward on the walls of that chamber as it gathers.
That is recharge.
And that is the thing moving beneath Mount St.
Helens.
Fresh magma working its way up from deep below and adding itself to the reservoir that feeds the mountain.
In the nearly two-month period before May 18, what was essentially happening at Mount St.
Helens was that magma or molten material was moving up from some deep reservoir beneath the mountain up into the volcano itself.
Now, you might hear that and think, well, a volcano filling up with magma sounds like exactly the thing you would worry about.
And you would not be wrong to think it.
But the single most important thing to understand about recharge is this.
Filling the tank and firing the tank are two completely different events.
And they can be separated by decades.
Can be.
Not always are.
Recharge tells you what the mountain is doing.
On its own, it does not tell you where that is headed.
Hold on to that because it is the question the rest of this story has to answer.
Here is how it works.
The magma beneath Mount St.
Helens pools in a reservoir somewhere between about 2 and 1/2 and 6 mi below sea level.
When fresh magma pushes up from beneath and joins that reservoir, the pressure inside rises.
That pressure squeezes hot fluids and gas out into the cracks of the surrounding rock.
Those fluids change the friction on tiny faults that had been sitting locked and still for years.
A fault that was stuck slips just a hair.
That slip is an earthquake, a very small one.
Then another crack slips and another scattered through the rock around the filling tank.
Hundreds of them.
Each one a tiny confirmation that something down there is adding pressure.
The hot sponge.
It helps to fix the picture you probably carry in your head of what that reservoir actually is.
Hear the words magma chamber.
And you probably imagine a glowing orange cavern waiting to overflow.
The reality is stiffer and far more important.
The reservoir beneath Mount St.
Helens is mostly solid rock with molten rock threaded through it.
It is less like an open pool and more like a hot sponge soaked with melt.
And a sponge behaves very differently from a pool.
A sponge absorbs, new magma can push into it, and the surrounding rock can soak up much of that change without heaving the crater floor upward.
That is one more reason a refilling volcano can shake deep below while its surface barely reacts at all.
It also explains why these particular earthquakes look the way they do.
They are small because nothing large is breaking.
This is the plumbing flexing under pressure, not a slab of the mountain giving way.
And they sit low, clustered around the reservoir a couple of miles down.
It was a beautiful blue sky day and the mountain was sitting out there and suddenly I saw this mushroom cloud go up above the volcano and climb rapidly up into the stratosphere.
You had to see it, to believe it, to get that total impression because that is where the work is happening.
They are not climbing toward the crater.
The magma is not marching up a staircase toward the door.
It is settling into the tank and leaning on the walls.
The numbers back that up.
Of those roughly 350 earthquakes in 2024, more than 95% were smaller than magnitude 1, far below anything you or I could ever feel.
The rate peaked in early June at around 38 earthquakes a week.
That is the sound of a system being fed.
But think about what being fed means.
Something is being added.
Pressure is being gained, not lost.
And a sponge can only absorb so much before it has to push back.
So if the tank really is filling, why on earth is the surface going down?
Why the surface is sinking?
That was the paradox we started with.
And the answer is the most revealing part of this whole story because it forces you to stop thinking of the mountain as a single object.
A volcano is not one thing and Mount St.
Helens least of all.
It is a tall system stacked in layers and those layers can do opposite things at the same time.
Far below sits the reservoir, the tank, the recharge zone, the place where fresh magma arrives and pressurizes the rock around it.
High above, near the top of the mountain, sits the young lava dome, the pile of fresh volcanic rock, the mountain built during its most recent eruption.
The one that ran from 2004 to 2008.
After that eruption ended, those two zones went their separate ways.
The lower reservoir began to reressurize, refilling in the dark.
That is what the earthquakes belong to.
The upper dome began to cool.
When fresh volcanic rock is still hot and full of trapped gas, it keeps changing.
It cools [music] and cooling rock contracts.
It releases its gas and rock that loses its gas settles.
It compacts under its own enormous weight.
Every one of those shallow processes pulls the surface above it downward.
That is the sinking.
Not the tank draining far below, but the lid slowly settling as it cools.
But notice what that means for you.
Watching from the outside, the one sign you would normally lean on for comfort, a surface that is going down instead of up, is being produced by the lid, not by the tank.
The lid is cooling, the tank is filling, and the calm you see on the surface is hiding the work being done underneath.
Which leaves one uncomfortable question.
How can anyone be sure which is which?
How we know?
The answer is that nobody is guessing from a webcam.
The shape of Mount St.
Helens is watched with a precision that borders on the absurd GPS receivers bolted directly to the rock track.
Their own positions using satellites overhead and [music] they can detect a shift of a few millime over a span of months less than the width of a pencil [music] eraser.
Tilt meters buried in the ground measure whether the surface is leaning the same way a carpenters’s level tells you whether a shelf is straight.
Radar satellites pass over the mountain again and again, comparing each image with the [music] last to see whether the land has risen or fallen by a fraction of an inch.
Layer all of that together and you get a continuous portrait of whether the mountain is breathing in or breathing out.
For years now, that portrait has shown a slow exhale.
So, the mountain is effectively keeping two separate accounts.
The lower account, the reservoir, is being credited as magma arrives.
The upper account, the Young Dome, is being debided as heat and gas leak away.
If you only read the surface, you would conclude the mountain is losing something.
Read both and you see it losing heat up top while gaining magma below, which is precisely what a volcano recovering from an eruption is supposed to do.
[music] Shaking while sinking is not a contradiction.
It is the fingerprint of recharge.
But a fingerprint only tells you who was in the room.
It does not tell you what they are planning to do next.
And there is something about those earthquakes that has convinced some people the official picture is not the whole picture.
One quick note before we go further.
Mount St.
Helens has its own chapter in our field guide covering the volcano itself and the hazard zones mapped around it.
The book is the breakpoint fault and volcano field guide and it covers every fault and volcano that can reach an American address along with how to check your own.
That is at breakpointstore.net and the link is in the description.
The earthquakes nobody counted.
Picture yourself on a busy morning at the mountain.
You pull up the raw seismic feed for Mount St.
Helens.
The same public live trace anyone can open.
The line scrolls across your screen and every so often it jitters.
A spike, a pause, another spike.
You start counting.
Then you open the official catalog of located earthquakes and the number there is smaller.
Much smaller than what you just watched with your own eyes.
What do you think next?
For a lot of people, the reflex is immediate.
If the ground moved dozens of times and the official count says only a handful, someone must be hiding something.
Grant the true part first because it is true.
There really are more events on the raw records than there are in the official catalog of located earthquakes, but the reason is geometry, not secrecy.
To formally locate an earthquake and assign it a magnitude, you need the same signal recorded cleanly at several stations so you can triangulate where it came from.
The way you might pinpoint a sound by hearing it from different corners of a room.
The very smallest events register on only one instrument, maybe two.
There simply is not enough information to place them.
A whisper heard by a single microphone cannot be located in a room.
Those events are not being suppressed.
They are unlocatable.
And here is what should end the darker version for good.
The scientists announced the uncounted events themselves.
When the monitoring network reported an earlier swarm at this mountain, it stated plainly that it had located more than 130 earthquakes and that there were many more too small to locate.
A coverup does not issue a statement reminding you that the real number is higher than the one it just gave you.
Better still, the raw traces you were counting are public.
They are live feeds, the very same records independent watchers use to count the extra events in the first place.
You cannot hide a signal and broadcast it at the same time.
So the shaking is honest and the sinking is real.
But honest data does not mean small stakes because what those tiny earthquakes are sitting on top of is far bigger than one chamber under one summit.
What lies beneath?
Why does this particular mountain draw so much attention when it stirs?
When identical tremors under a calmer peak would barely make the news.
Part of the answer is history and we will come to that.
But part of it is what sits underneath.
Mount St.
Helens is the youngest and most active volcano in the Cascade Range.
The long line of peaks standing back from the Pacific Northwest coast from Northern California up into British Columbia.
It is the busiest, the one most likely to do something within a single human lifetime, possibly within yours.
To understand what feeds it, scientists launched a research project called Mush, short for imaging magma under St.
Helens.
Over several years, the team set off two dozen controlled underground explosions and spread thousands of seismometers across the landscape, building a picture of what lies beneath the mountain.
What they found is not a single balloon of magma waiting under the summit.
It is a network, an upper reservoir made of several connected bodies, a composite structure stretching from a few miles down to roughly 9 m below the surface and several miles across.
Below that sits a separate zone of partly molten rock where only a small fraction of the material is actually liquid.
And the plumbing traces all the way down toward the base of the crust more than 25 m beneath the surface.
This mountain does not sit over a pool.
It sits over a system.
And that system is refilling from the bottom up.
Which leaves you with a simple question.
Refilling from what?
The engine offshore.
That system has a source.
And the source is not directly under the mountain.
It is out beneath the ocean.
Off the coast of the Pacific Northwest, a slab of seafloor called the Juan Defuca plate is being forced beneath the edge of North America and dragged down into the hot interior of the planet.
As that slab sinks, the water locked inside its rocks is cooked out by rising heat and pressure.
That water rises into the hot rock above it, and water does something remarkable to rock.
It lowers the melting point just enough to turn solid rock into magma.
That magma lighter than the rock around it begins to rise.
It feeds the volcanoes above.
Line up every place where this is happening and you get the Cascade [music] Range.
Mount Baker, Glacier Peak, Mount Reineer, Mount Adams, Mount Hood, and Mount St.
Helens.
The most restless of them all.
This machine runs on a clock measured in millions of years, and it never switches off.
The plate keeps sinking.
The water keeps rising.
The rock keeps melting.
That is why there is always something to refill the reservoir under Mount St.
Helens.
And it is also why a busy stretch of small earthquakes on its own does not move the mountain one inch closer to erupting.
But sit with the other half of that for a second.
A machine that never switches off never stops loading either.
Every year more arrives.
So [music] what has this mountain done with all that magma before?
It has a track record and it is the part almost nobody remembers.
It has happened before.
Mount St.
Helens did nearly this exact thing 10 years ago.
Beginning around the middle of March in 2016, the seismometers under the mountain began picking up small earthquakes at a rising rate.
Over about 8 weeks, the network located more than 130 of them and openly noted that there were many more too small to locate.
Those quakes were tiny, most of them magnitude 0.5 or smaller.
They sat roughly 1 to four miles down right around the reservoir.
Even as the rate climbed toward about 40 located earthquakes [music] a week, there was no rise in volcanic gas, no swelling of the surface, no migration of earthquakes upward toward the crater.
The scientists called it recharge.
And they said something worth repeating plainly.
Recharge can continue for many years beneath a volcano without leading to an eruption.
Nothing erupted, and 2016 was not a one-off.
The mountain had done the same thing for far longer stretches before.
It refilled through the late 1980s and across the 1990s in sequences that ran on for years and led to nothing.
Before its 2004 eruption, Mount St.
Helens spent something like 18 years recharging, stirring, settling, and going nowhere.
That is the tempo of this mountain.
Recharge is not a fuse burning down toward a fixed moment.
It is closer to a slow heartbeat.
And the gap between filling and firing can stretch across decades.
If you live in the valleys below, that history is [music] the whole point because the same signature has now repeated.
The rise in activity across 2023 and 2024, the biggest jump since 2008, was read the same way as 2016, and it faded the same way.
But here is the catch.
Fading is not the same as finishing.
Those 18 years of stirring and settling that went nowhere did not go nowhere forever.
At the end of them came 2004.
[music] A heartbeat never tells you in advance which beat is the last calm one.
And sometimes the mountain does not even need to erupt to send people into a panic.
The ghost plume.
On the 16th of September 2025, people looking up at Mount St.
Helens saw gray plumes rising off the summit.
If you knew this mountain’s history, it was a chilling sight.
And the Geological Survey had to step in and tell people plainly that the mountain was not erupting.
Those plumes were not fresh ash.
They were ash from 1980, some 45 years old, lying loose across the flanks of the volcano and lifted into the sky by strong winds.
The mountain had thrown up a ghost of its last eruption and for a few hours worn the costume of a new one.
This is a mountain that can fool people while standing in plain view.
And knowing that is its own kind of protection.
Which brings us to the strange gift buried in all of this.
What 1980 really looked like.
Because scientists have watched Mount St.
Helens erupt twice within living memory.
They can describe what its next eruption will most likely look like.
Not vaguely, but by style, by path, and by target.
Start with what is unlikely.
The catastrophe of 1980.
On the morning of May 18th, 1980, the entire north flank of Mount St.
Helens, which had been bulging outward at around 5 ft a day, collapsed in the largest landslide in recorded history.
With that flank suddenly gone, the pressurized magma behind it was unccorked sideways.
A lateral blast tore across the landscape at speeds of at least 300 m an hour, flattening forests across hundreds of square miles.
57 people were killed.
What is easy to forget is that 1980 came with two full months of warning.
The earthquakes began in March and they did not stay deep.
They climbed toward the surface.
A steam blast tore open the summit in late March.
The ground hummed and the north flank swelled visibly day after day until the whole side of the mountain was pushing outward like something alive.
A young geological survey scientist named David Johnston was stationed at an observation post about 6 miles away when the blast came.
His last radio call, Vancouver, Vancouver, this is it, has echoed through volcano science ever since.
That was a real countdown.
Loud, public, and impossible to miss.
None of it is happening now.
And there is a structural reason a repeat of that specific catastrophe is considered unlikely.
The sideways blast of 1980 needed a tall, intact flank standing over pressurized magma.
A wall that could bulge, fail, and aim the explosion outward.
The 1980 eruption blew that wall away and left a vast horseshoe-shaped crater in its place.
The setup that pointed the explosion sideways no longer exists in the same form.
So if the next eruption will not look like 1980, what will it look like?
The answer is an eruption that happened in your lifetime and that you have very likely forgotten.
The eruption nobody remembers.
In September of 2004, after those 18 years of on andoff recharge, Mount St.
Helens came back to life.
Not with a bang, but with a push.
Thick, sticky lava began squeezing up into the crater, at times at a rate of roughly a dump truck load every second, and it kept going for three and a half years.
The lava was so stiff it came out almost solid.
Seven successive spines rose from the crater floor, each one crumbling and being shoved aside by the next, together, building a brand new dome hundreds of feet tall inside the crater of 1980.
That slow dome building eruption is the template for what comes next.
It is hazardous close to the mountain.
It can throw up ash that threatens aircraft.
But it is not a regional catastrophe and it is [music] not a repeat of 1980.
Which leaves the question that matters most if you live anywhere near this mountain.
If the next one started, would anyone see it coming in time?
The five signs.
Very likely yes, because scientists know what a real countdown looks like.
Five things would begin to change together.
First, the earthquakes would move.
Instead of clustering deep around the reservoir, they would begin climbing upward toward the crater.
Second, the character of the shaking would change.
The sharp separate pops of cracking rock would give way to a continuous hum, a signal called tremor, the sign of fluid actually on the move.
Third, the sinking would stop.
[music] The surface would reverse direction and begin to rise as the pressure below finally outpaced the settling above.
Fourth, the gas would climb.
Carbon dioxide and sulfur dioxide would increase as magma drew closer to the surface and released what it [music] carries.
And fifth, steam blasts would begin tearing at the crater, just as they did in the spring of 1980.
What matters is not any one of those flickers on its own.
What matters is several of them building in the same direction at the same time.
Today, not one of the five is present, but those five signs only warn you about an eruption.
And the thing most likely to reach the towns below this mountain [music] does not need an eruption at all.
The real danger is water.
The next eruption when it comes is most likely a calm, slow one.
But calm does not mean harmless.
And the real danger around Mount St.
Helens has never been the part you picture.
It is not the blast.
It is water.
The greatest threat to life and property in the valleys around Mount St.
Helens is a laahar, a volcanic mud flow.
When heat, an eruption, or even a simple collapse of loose material mobilizes the snow, ice, and debris on the mountain, it can turn into a fastmoving river of mud and rock with the consistency of wet concrete.
And Mount St.
Helens is loaded with fuel for them.
The vent and the growing dome are wrapped by Crater Glacier, a young glacier that formed inside the crater after 1980.
The crater floor and flanks hold enormous volumes of loose volcanic rock.
And every winter, thick seasonal snow pack piles on top of it all.
A laahar does not need a giant eruption to begin.
It needs material and a push.
And once they start, these flows travel.
Past laahars from this mountain have run 30 to 60 miles from their source, pouring down the river valleys and repeatedly reaching all the way to the Colombia River by way of the Tudel, the Cowitz, the Kalama and the Lewis.
In 1980, mud flows surged down the Tutti River, tore out bridges and homes, and dumped so much sediment into the Colombia that the shipping channel was choked and ships were stranded up river.
The forecast is not abstract.
It has a map and towns sit on that map.
And it is why the monitoring matters so much.
Not because the mountain is about to blow, but because the warning time for a mud flow can be measured in minutes.
And the communities in those valleys depend on getting every one of those minutes.
The lake that cannot drain.
There is a second hazard here that you have probably never heard of.
One that the 1980 eruption created then left behind and that remains unresolved 46 years later.
When the north flank collapsed in 1980, the debris avalanche did more than reshape the mountain.
It buried and blocked the natural outlet of Spirit Lake.
The lake sitting at the foot of the volcano.
Water kept flowing in from rain and snow melt, and the level kept rising, held back only by a massive plug of loose avalanche debris.
A lake with no way out and a wall of rubble holding it back is a slow motion disaster waiting to happen.
So in 1984 and 1985, the Army Corps of Engineers boarded a tunnel roughly a mile and a half long through solid bedrock, draining the lake in a controlled way into a nearby creek.
That tunnel is now the only thing keeping Spirit Lake in check.
The lake is deliberately held well below the point where it could over top the debris blockage, but the tunnel runs through unstable ground, and shifting rock has damaged it more than once.
It needed major repairs in the mid 1990s and again roughly a decade ago.
The Forest Service, the Army Corps, and the Geological Survey have been working toward a permanent solution because the stakes are plain.
If the debris dam holding back Spirit Lake ever failed, it would send a torrent of water and debris down into the same Toodel and Cowitz valleys that Lahar’s already threaten.
The last eruption is not finished with those valleys.
Its unfinished business is still sitting up there, held back by a tunnel that keeps needing repairs.
Where the mountain stands now.
So where does all of this leave Mount St.
Helens today?
[music] Right where it has been, measurably alive, refilling in the dark, sitting at the lowest alert level there is.
The earthquakes are small and they are staying deep.
The surface is cooling and settling.
The gas is calm.
Every box on the real countdown checklist is still empty.
That is what scientists have detected moving beneath Mount St.
Helens.
Not a mountain about to explode, but a mountain doing the slow, patient work of refilling.
The same work it did in 2016 and through 2023 [music] and 2024.
But none of that is a promise.
Mount St.
Helens has stood down again and again in 2016, in 2023, in 2024, and it will almost certainly stand down from this stretch of recharge, too.
Almost certainly.
It is still the most active volcano in the Cascade Range, sitting above a plate that never stops sinking, fed by a system that never stops running.
It does not stay calm forever.
It has stood [music] down every single time right up until the one time it will not.
The one measurement to watch.
So here is the single measurement worth watching.
The one that separates every calm year from the beginning of the end.
Not the raw earthquake count.
That number will rise and fall.
And on its own it tells you surprisingly little.
Not a plume of gray over the summit because you now know the wind can fake that.
Watch the shape of the mountain.
Today it is sinking.
The lid is cooling, settling, slowly, exhaling over a tank that is filling far [music] below.
The day the sinking stops and the surface begins to rise is the day the mountain stops filling and [music] starts to move.
That is the threshold.
Until then, the shaking is not a warning.
It is the sound of a volcano being [music] exactly what it is.
Would you live in the Toodel Valley knowing what you know now?
Tell us in the comments and subscribe so you’re here the day the mountains shape changes.
