MS-ESS2-2. Construct an explanation based on evidence for how geoscience processes have changed Earth’s surface at varying time and spatial scales.
Key Vocabulary: volcano, subduction, eruption, pyroclastic flow, magma, lava, crust, tectonic plate, silica, melting point, lahar
For the last couple decades, Volcán de Fuego, a volcano in Guatemala, has been in a continuous period of low-level activity. But on June 3, 2018, Volcán de Fuego unexpectedly erupted on a scale not seen since 1902. The eruption sent a column of ash several miles into the sky and pyroclastic flows more than 10 km down the side of the volcano. As of June 12, 114 people have been confirmed dead, at least 300 injured, at least 192 persons missing, and thousands have been evacuated.
Volcanoes have been something of a hot topic lately. Kilauea in Hawaii has been continuously erupting for about a month. But while lava flows in Hawaii have destroyed hundreds of homes, there have thankfully been no fatalities reported. So what caused the disparity in devastation? There are some key differences between Kilauea in Hawaii and Volcán de Fuego, such as magma content, eruption style, and the type of volcano that make the eruption in Guatemala far more deadly.
Volcán de Fuego is one of the most active volcanoes in Central America. Unlike the ongoing eruptions of Kilauea in Hawaii, which geologists anticipated and were able to give early warnings to residents, Volcán de Fuego was a sudden, explosive eruption. This is the result of the different origins of each volcano; Kilauea formed from hotspot volcanism whereas Volcán de Fuego is related to the subduction of a tectonic plate.
Subduction occurs at convergent plate boundaries where one plate is pushed underneath another. Due to their higher density, oceanic plates will dive or subduct under the more buoyant continental plates. An example of this is in the northwest United States, where the Juan de Fuca oceanic plate is being subducted beneath the continental North American plate under the states of Washington, Oregon, and Northern California, all of which are home to several active volcanoes.
But why do volcanoes form at these subduction zones? Oceanic plates are very rich in water; when the crust forms at divergent plate boundaries, seawater reacts with the minerals in the rock. The water becomes trapped in the plate as it moves along. Once the water-rich plate begins to subduct, it encounters the high temperatures and pressures of the Earth’s interior, driving the water out of the sediments and rocks into the dry, hot mantle above. This process lowers the melting point of the mantle rocks, allowing the mantle to partially melt into new magma. This magma rises to the surface and eventually erupts to form a volcano. The continued subduction of the plate supplies the magma chamber for volcanoes and future eruptions.
Nearly 75% of the world’s volcanoes surround the Pacific Ocean, an area known as the “Ring of Fire” and where several oceanic plates are subducting. Guatemala sits above one of these subduction zones, where the Cocos plate is being subducted beneath the Caribbean plate, forming a volcanic arc extending over 1000 km and is home to several active volcanoes.
What made this eruption so deadly?
One of the main reasons Volcán de Fuego’s eruption was so devastating is due to the type of the volcano, the magma that feeds the volcano, and how well the magma flows. Volcán de Fuego is a cone-shaped volcano (stratovolcano) that tends to be very large with steep slopes. This type of volcano is formed from a magma that does not easily flow, similar to thick oatmeal. As a result, when the magma erupts, it does not travel far from the volcano’s vent, building a cone-shape overtime. The magma also as a higher silica content, which traps gases and water vapor, causing pressure to build up until eventually, the volcano erupts explosively. Like shaking a soda can before opening it, the violent explosion sprays material everywhere.
The resulting explosion creates a column of hot ash high into the sky. Once this eruption column cools, it becomes too dense to continue its upward movement, so it can collapse and form a pyroclastic flow. A pyroclastic flow is a very hot (typically >1300 °F) cloud-like mixture of rock fragments, gas, and ash that moves very fast (700km/hr or 430 mi/hr) down the side of the volcano, destroying just about everything in its way. Additionally, if a pyroclastic flow mixes with water, it can form a mudflow called a lahar, which moves like a flood of concrete. Kilauea, on the other hand, is formed from a magma that flows more easily (like honey) due to its high temperature and low silica content. This causes a broad, dome-shaped volcano or shield volcano to form as the fluid-like lava can flow far from the vent of the volcano. The content of the magma is also why Kilauea’s eruptions tend to be rather quiet and less violent by comparison. The gases in the magma don’t build up enough pressure as they can easily escape from the fluid-like magma and they don’t get trapped like they do in the thick, oatmeal-like magma.
Additionally, Volcán de Fuego is located near a densely populated area. The villages at the base of the volcano had no warning or time to escape. Kilauea, however, is located in a National Park, away from populated areas. The people whose homes were destroyed by lava flows in Hawaii had ample warning and time to evacuate. Volcán de Fuego is also not as well monitored as Kilauea, with only one device to record earthquakes and none to measure gas and ground deformation. The lack of roads and infrastructures makes Volcán de Fuego difficult to access and to keep instruments up and running full time. Because Volcán de Fuego always has an increased level of volcanic activity, it was difficult to see when the volcano went from a quiet state to a state of increased activity which would typically indicate a future eruption.
Over 1.7 million people have been affected by the eruption and ashfall. Official search and rescue has halted due to an additional eruption and rainfall has mixed with the ash from the pyroclastic flows to form lahars, but family members and volunteers continue to search for survivors. More than 4,000 people remain in shelters as their homes and livelihoods have been destroyed. People from around the world are sending donations and volunteers to help to aid in the relief.
Even though scientists were well aware an eruption at Kilauea was imminent, the sudden tragedy at Volcán de Fuego shows that there is still more that needs to be understood about volcanic processes and hazards. The devastating event in Guatemala further highlights the importance of studying and monitoring volcanoes around the world to help develop ways to predict volcanic eruptions more accurately, so as to prevent casualties and minimize damage by providing ample warning and allowing for timely evacuations. Furthermore, it is important to inform people about what the different types of eruptions are and how dangerous volcanoes can be such that people are able to recognize the risks and know what to do to stay safe.