Comparing the Active Volcanism in Hawaii and Guatemala

Figure 1a and 1b. The image on the left is of the basaltic lava flows in Hawai’i, while the image on the right is of the pyroclastic flow in Guatemala. (Image of Hawaiian flow from USGS and image of Fuego pyroclastic flow from Calgary News).

The Hawaiian volcano Kilauea and the Guatemalan volcano Fuego have gotten a lot of media attention recently due to active eruptions that directly impact people. However, their overlapping occurrences are about the only similarities that these volcanoes share. The geology and hazards of these volcanoes are dramatically different. Kilauea is in the news because it is erupting slow moving (~13 feet per hour) basaltic lava, spewing 200-foot tall lava fountains, and periodically producing localized steam explosions (Figure 1a). Fuego is in the news not because of a lava flow, but because explosive volcanic activity triggered an avalanche of hot rocks and gas. This geologic phenomenon is called a pyroclastic flow and in Fuego it traveled more than 50 miles per hour straight toward a heavily populated community (Figure 1b). Due to its speed and destructive force, pyroclastic flows are much deadlier than basaltic lava flows. The latest death toll for Fuego is 114 people, with reports from the Kilauea eruption describing one man having sustained serious injuries on the ground and injuries to another 23 people who were in a boat observing the lava enter the ocean. Pyroclastic flows are not lava flows, but can be described as a landslide of hot cement and toxic gas that is caused by active volcanism.

Other differences in the two volcanoes are that Kilauea is a shield volcano fed by a hot spot of magma rising from the mantle to the surface, while Fuego is a stratovolcano fed by the collision of two tectonic plates (view Figure 2). At Fuego, the tectonic plate under the ocean is actually sliding under the plate that Central America is sitting on. As the lower plate sinks, it heats up and releases water into the rock above, reducing the melting temperature of that rock and creating a chain of volcanoes. The differences in how the magma is created for these two types of volcanoes has a significant impact of the chemistry of the magmas and how they are able to behave. In Figure 2, the clearest distinctions between the two types of volcanoes are the overall shape and the steepness of their slopes. Steeper slopes tend to be more unstable and allow material to travel faster downhill, such as the case in Fuego’s stratovolcano.

Figure 2a and 2b. The image on the left is of a shield volcano, note the gentle slopes. The image of the right is of a stratovolcano, note the steeper slopes. (GHS)

The differences between these volcanoes are linked to their lava compositions. Both volcanoes’ magmas have varying amounts of gas and the compound silica, which affect the overall consistency and therefore behavior of the lava. Lava that is poor in silica and gas, such as the basalts erupting from Kilauea, flow more easily like ketchup forming overall more dome-like shapes. However, the silica- and gas- rich lava of Fuego, tends to build-up and explode instead of flow forming more cone-like shapes.

The increase of media coverage for these volcanoes does not mean that there is any substantial increase of volcanic activity at either location, or that these volcanoes are in some way connected. According to the U.S Geological Survey there are over 1,500 potentially active volcanoes worldwide with a handful of volcanoes erupting daily.