Of all of the active volcanoes in the United States, there is a single system which I hope
to never see erupt in my lifetime.
I do not mean the Yellowstone volcano in Wyoming, or even the densely populated Clear Lake volcano
in California.
Rather, I am referring to the towering Mount Rainier, as a future eruption of this volcano
in a worst case scenario could cause tens of thousands of casualties and billions of
dollars in damage.
The reason why this towering peak is so potentially dangerous relates to one simple word; lahars.
Per a direct quote from the U.S. Geological Survey, "A lahar is a hot or cold mixture
of water and rock fragments that flow quickly down the slopes of a volcano.
They move up to 40 miles per hour through valleys and stream channels, extending more
than 50 miles from the volcano.
Lahars can be extremely destructive and are more deadly than lava flows."
While this description might make it sound like lahars are simply a typical flash flood,
what this definition leaves out is that lahars often overtop the river channels they are
in and spread out to surrounding higher ground which is not ever effected by flash flooding,
reaching heights of up to 50 meters or 164 feet and bulldozes everything it encounters.
Lahars act like a fast moving wall of concrete, and since the beginning of the 16th century
have caused approximately 56,000 fatalities at various volcanoes around the globe.
Factors such as a tall volcano height, heavy glacial cover, and significant hydrothermal
alteration are all factors which aid in the generation of lahars, and Mount Rainier has
all 3.
Today, more than 150,000 people live and work on top of lahar deposits which Mount Rainier
deposited during the last 10,000 years, and just so you can understand how significant
of an area would be at potential risk were a volcanic eruption to occur, I have overlaid
this map.
The purple represents the area devastated by a lahar in the year 1500, the pink represents
part of the area effected by a lahar around 100 BCE, and the largest of the group, aka
the yellow represents the massive Osceola lahar which was produced in the year 3600
BCE.
This is why if you live in Puyallup, Auburn, Buckley, or a select number of other local
cities, if you were to dig down, look in a local roadcut, or see a rock layer that is
primarily brown but also a mixture of yellow and orange, then you are looking at an area
impacted by this prehistoric Osceola lahar.
This Osceola lahar material is partially composed of remains of Mount Rainier itself, as at
the beginning of the explosive eruption which eventually formed this lahar, Rainier was
1100 feet taller.
This additional height is no longer present on Rainier, as it collapsed as part of a massive
landslide which generated the Osceola lahar.
The good news is that such large scale lahars generally but not always occur as the result
of a volcanic eruption.
And, if Mount Rainier was to erupt again in the future, there is also a chance that no
lahar or only a small scale lahar occurs which only impacts areas within Mount Rainier National
Park.
Among Cascade Range stratovolcanoes, Mount Rainier is quite an old complex as it began
forming 500,000 years ago.
Its first eruption occurred in the remains of an older highly eroded stratovolcano that
stood in its place between 1 and 2 million years ago.
This initial eruption produced blocky flows of andesite lava, generated pyroclastic flows
which traveled towards the north, and constructed a new volcanic cone.
Over the next 80,000 years, Rainier erupted at a very high rate, building itself close
to its modern height and emplacing about 50% of the material it has ever erupted.
Eruptions during this period constructed the peaks of Old Desolate and Burroughs Mountain.
Between 420,000 and 280,000 years ago, Rainier produced very few eruptions and the eruptions
which did occur were generally quite small.
During this period, the mountain's summit became highly eroded with glaciers carving
deep valleys on its flanks, much like its modern day appearance.
Between 280,000 and 160,000 years ago once again saw an increased eruptive rate, rebuilding
the summit and creating fairly long reaching andesite lava flows such as what created Klapatche
Point.
Eruptive activity then decreased again, but between 160,000 and 40,000 years ago several
north flank vents were created that erupted more fluid basaltic andesite lava flows.
The lavas found on Mount Rainier's summit region have been emplaced since then.
Since 10,000 years ago, every single one of Rainier 23 eruptions have occurred at its
summit crater.
The largest of these recent explosive eruptions occurred in 250 BCE in an event which was
about 15% the size of the 1980 eruption of Mount Saint Helens.
While some sources claim that Mount Rainier's last eruption occurred around 1500, there
are several reports of gray smoke originating from this volcano during the 1800s, possibly
indicating that small phreatic eruptions occurred.
The last such report occurred in 1894.
While Mount Rainier has not erupted in at least a century, perhaps as much as 5 centuries,
it is almost certain to one day erupt again, especially due to the fact that it has produced
the second highest number of volcanic eruptions of any volcano in the lower 48 states during
the Holocene epoch.
As a result of the hazards associated with this volcano, in their most recent volcano
hazard assessment, the U.S. Geological Survey designated Mount Rainier as a very high threat
volcano.
As a final note, I would like to thank my YouTube channel member Howie B for upgrading
their membership tier to this channel!