Costa Rica is known for its scenic national parks, and tropical wildlife such as Toucans. However,
it also has a number of active volcanoes. One of these volcanoes has a near symmetrical shape,
and is responsible for a continuous eruption from 1968 to 2010. The volcano I am referring to is the
Arenal Volcano, which has produced some of the nation's largest volcanic eruptions in recent
history. This video will discuss this active volcano, and mention what its future hazards are.
The Arenal volcano can be found in the northwest portion of Costa Rica in the province of Alajuela.
Specifically, it is 7 kilometers west of the town of La Fortuna. The volcano exists due to the
subduction of the Cocos tectonic plate underneath the Caribbean plate. The subducted crust from this
collision then melts and migrates upwards until it erupts on the surface, creating a volcano.
The Arenal volcano is a stratovolcano which today is 1,670 meters tall.
The first eruption from this volcano occurred only 7,000 years ago,
and built a portion of the volcano's base with largely basaltic andesite lava. This
eruption was also quite explosive, as it left a definable layer of ash in the surrounding areas.
We have since inferred that this eruption was the first of many highly explosive eruptions called
plinian eruptions. A Plinian eruption is an eruption type defined by its similarity
to the famous eruption of Mount Vesuvius in 79 AD. When these eruptions occur at
the Arenal volcano, it produces several hundred million cubic meters of tephra.
Since the first eruption in 5060 BC, 18 other plinian eruptions have occurred at this volcano.
For example, a similarly sized eruption occurred in 3900 BC and then again in 3350 BC.
In 3190 BC, the Arenal volcano produced an eruption at the neighboring stratovolcano
known as Cerro Chato. This feature can be found 2.8 kilometers to the southeast of the main peak.
Cerro Chato erupted again in 1770 BC, and has not erupted since.
After this feature stopped erupting, plinian eruptions became more frequent. The interval
between these eruptions dropped from about once every 700 years to about once every 235 years.
These large eruptions continued until 1400 AD, when the last of these large eruptions occurred.
I want to note that until quite recently, we thought that Arenal had been quiet for
several hundred years between 1400 and 1968. However, this was not the case.
During this period, 4 volcanic eruptions occurred but they were several orders of magnitude
smaller than the prior Plinian eruptions. The volcano subsequently came back to life in an
explosive eruption on July 29th, 1968. Many locals in the area thought that the volcano was extinct,
and were caught off-guard. During the early stages of the eruption, superheated rock and gas
known as pyroclastic flows raced downhill and reached several kilometers away. The volcano also
ejected large boulders more than a kilometer away. This eruption continued at lower intensities for
several decades. It did not take long for these eruptions from Arenal to become a
tourist attraction due to the beautiful glow of the lava erupted on its steep slopes.
For 42 years, the eruption from Arenal was near continuous until it ceased in December of 2010.
The Arenal volcano is almost certain to erupt again, although we don't know exactly when the
next eruption will be. When the next eruption occurs, it will once cause a variety of hazards.
The three main hazards from this volcano are lava flows, pyroclastic flows, and lava bombs.
Pyroclastic flows are the deadliest of the hazards, and could reach areas up to
10 kilometers away. Lava flows are not as deadly due to their slow movement speed,
although they could eventually travel up to 5 kilometers away and destroy structures.
The volcano can also violently eject pieces of lava, which on occasion have been thrown more
than 2 kilometers away. Although a future eruption could pose a risk to the town of La Fortuna, it
should be safe for the next several hundred years. I hope that you enjoyed this video! If you would
like to request a specific topic, please leave a comment below.