In the scenic mountain town of Mammoth Lakes within California, it was another peaceful
day and the date was may 25th 1982.
But then, there was a sort of commotion.
Neighbor talked to neighbor, noting that a widely distributed newspaper contained an
article that a volcano few had ever heard of right next to the town was about to be
placed at a raised alert level.
Soon, tabloid sources picked up the story, issuing blatantly incorrect statements, claiming
that an eruption at the Mammoth Mountain volcano was imminent, only days away, potentially
devastating the 7,000 person town of Mammoth Lakes.
People soon panicked, with many leaving the town, and businesses closed.
While magma was advancing upwards towards the surface with an epicenter 2.5 miles southeast
of the town, the nature of this event was blown far out of proportion.
As, originally, the United States Geological Survey had planned to issue a so called "notice
of potential hazard" which in terms of the modern scale would roughly equate to a volcano
alert level halfway between green and yellow.
They planned to accurately discuss the potential volcanic threat on their terms, but instead
the information was leaked to the press 3 days early.
This leak was likely owed to the fact that this volcanic unrest was the first event to
occur since the destructive 1980 eruption of Mount Saint Helens whose destruction and
impact was far larger than the majority of volcanologists thought would occur beforehand.
Yet, as 1982 turned into 1983, and 1983 turned into 1984, a volcanic eruption did not occur.
So, what exactly happened that year, and how close were we to an actual volcanic eruption?`
For context, there is a 30 mile chain of volcanic vents which stretches from several miles south
of Mammoth Lakes at a series of two red topped cinder cones all the way north to a series
of vents within Mono Lake.
This chain consists of three separate volcanoes that each encompass a series of vents, which
altogether have erupted more than a dozen times in the last 10,000 years.
To the east of Mammoth Mountain is the vast caldera of the Long Valley Caldera supervolcano,
where the entire 20 mile wide depression represents a collapsed mass of ground that sunk up to
3,000` feet after a massive eruption from this volcano 760,000 years ago.
All of the Long Valley Caldera's eruptions since this caldera collapse have been several
orders of magnitude smaller, with the last such event occurring 16,000 years ago.
With all of this taken into account, in 1980 a magmatic intrusion occurred not at Mammoth
Mountain like what was first believed but rather within the Long Valley Caldera.
This first became evident on May 25th, when two magnitude 6 earthquakes struck within
the caldera, soon being followed by hundreds of earthquake aftershocks.
As at 5 miles or 8 kilometers depth, a new batch of magma was pushing up the central
region of the caldera, causing the ground to rise by 10 inches in 10 months.
However, this activity would wane until 16 months later when a magnitude 5.9 earthquake
struck.
This earthquake was caused by changing stresses related to another intrusion of magma which
had forced it ways upwards, going from 8 to 4 kilometers depth by June of 1982.
This intrusion then stalled and solidified at depth, never to move again.
In truth, we in my opinion were four months away from a volcanic eruption occurring within
the Long Valley Caldera which likely would had an explosive component to it.
Then, in 1989, a deeper magmatic intrusion occurred, but this time directly beneath the
Mammoth Mountain volcano, where a 60 million cubic meter batch of magma migrated upwards
before completely ceasing its upward motion at a depth of 15 kilometers or 9.3 miles.
As this magma solidified, it began degassing large volumes of carbon dioxide gas.
This gas was carried upwards until it was emitted onto the surface via a series of minor
fault lines, seeping into the soil and pooling at low points.
This caused sections of the forest to die and turn brown, with no new vegetation growing
within it thereafter due to the 300 tons of carbon dioxide being released each day.
While trees need carbon dioxide to grow, too much is lethal to them.
To this day this degassing has continued, although at an ever decreasing amount on sections
of Mammoth Mountain.
Luckily, this 1989 intrusion was never remotely close towards actually triggering a volcanic
eruption.
Due to these events and the later 1989 to 1990 eruption of the Redoubt volcano in Alaska,
the USGS overhauled their old rating system, replacing it with a more modern 4 color code
system that it easier to comprehend.
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on YouTube!