On June 28th, 2021, at 5:42 am in the morning, one of the most active volcanoes in Costa
Rica produced a new eruption.
As this volcano erupted, a series of pyroclastic flows raced across the landscape, traveling
3000 meters before they stopped.
Since a large volume of ash was ejected, a tall ash plume rose two kilometers into the
sky.
What had just occurred was one of the largest eruptions from the Rincon de la Vieja volcano
in the last century.
However, if you look at the geologic history of this volcano, it has produced far larger
explosions in the past.
This video will discuss this volcano, and mention what its future hazards are.
The Rincon de la Vieja volcano can be found in the northwest portion of Costa Rica.
Specifically, it is 23 kilometers north northwest of the town of Liberia.
The reason why this volcano exists is due to the collision of two tectonic plates off
the west coast of Costa Rica.
There, the Cocos tectonic plate is being subducted underneath the Caribbean plate.
The melted crust from this collision then migrates upwards, before erupting on the surface,
thus forming a chain of volcanoes.
This subduction related volcanic activity had been ongoing where Rincon de la Vieja
is today for approximately 8.5 million years.
During the last 2 million years, three successive supermassive eruptions occurred, each of which
created eruptions thousands of times larger than the largest eruption of la Vieja.
These supermassive eruptions ejected such a large volume of magma, that it caused the
ground underneath them to collapse to fill the void left by an empty magma chamber much
like a sinkhole.
This created a group of three overlapping calderas, of which one is 15 kilometers wide.
Since the formation of this large caldera, magma has slowly refilled much of its underlying
magma chamber.
Over time, this pushed the ground upwards, allowing magma to travel upwards and erupt
onto the surface, thus forming the Rincon de la Vieja volcanic complex.
Although we aren't exactly sure when this volcanic complex began forming, several eruptions
had occurred by 295,000 years ago.
These eruptions started to build the first of what would later become 9 volcanic cones
out of a gray rock type called andesite.
Infrequent large volume eruptions produced the majority of rock on these volcanoes, while
infrequent phreatic eruptions from their main vent produced additional ash close to their
summits.
Over time, the active vents in this complex have slowly moved to the southeast.
As an example, the west crater is a highly eroded former summit crater cut away by erosion.
To the east are two highly active craters called Von Seebach Crater and "the active
crater".
Since at least 5,000 years ago, all of the eruptions at this volcano have occurred from
the same vent, including its most recent eruption.
These eruptions all originated from what is termed the active crater.
Ash from these eruptions can be seen coating the ground in a several kilometer radius.
Although this volcano has produced numerous recent eruptions, it hasn't actually erupted
any lava for more than 3,000 years.
The last major eruption occurred in 1820 BC, which created a towering ash plume and coated
the summit with up to 20 meters of ash.
Most of the eruptions which occur today are the result of at depth magma heating groundwater
causing it to flash to steam and explode.
Since 1998, this volcano has produced 10 different eruptive sequences.
So, will this volcano erupt again, and what is my analysis of its most recent eruption?
In the next few weeks, I predict that more phreatic eruptions will intermittently occur
every few days, although these will be a fraction of the size witnessed on June 28th.
However, these small eruptions can still be quite dangerous, as they can both eject boulders
of rock in a several kilometer radius but also produce small pyroclastic flows.
Additionally, residents in the area need to be cautious during the next series of heavy
rainstorms.
When the next storm occurs, it will dislodge much of the recently ejected ash, causing
it to flow downstream with a viscosity of concrete in a phenomena called a lahar.
These lahars will effect low points adjacent to the volcano, potentially taking out nearby
roads and bridges.
On average, Rincon de la Vieja produces a sustained eruption about once every five years,
so more similar explosions will occur in the future.
While the volcano is still in danger of erupting without warning, I recommend not allowing
anyone to get near its summit.
I hope that you enjoyed this video.
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