In March, a team of U.S. Geological Survey scientists, including two from Hawaiʻi, visited El Salvador for volcanological field studies and a workshop on lava flow hazards.
Exchanges like this help to improve awareness of volcanic hazards in other countries, and they enable the USGS to better understand volcanoes in our own backyard.
El Salvador is the smallest country in Central America, sitting on the Pacific coast and measuring slightly larger than all of the Hawaiian Islands combined.
But the eight main Hawaiian Islands are comprised of only 15 volcanoes above sea level. El Salvador has more than 200. And that’s with a population of about 6 million people, about four times as many as Hawaiʻi.
There are numerous volcanoes in El Salvador because it sits along the Central American volcanic arc, rather than atop a hotspot like Hawaiʻi.
Volcanic arcs form where an oceanic tectonic plate subducts beneath either a continental plate or another oceanic one. The ocean crust triggers melting as it dips into the Earth’s mantle, creating magma that rises to the surface through the overlying plate.
Though El Salvador has five larger volcanoes with historical eruptions, numerous fault lines allow magma from the subduction zone to emerge just about anywhere. This has resulted in hundreds of smaller volcanoes, most of which have erupted only once.
Volcano monitoring in El Salvador is handled by the Ministerio de Medio Ambiente y Recursos Naturales. In addition to tracking the weather and other natural hazards, a small team of volcanologists works to study the geological and geophysical dynamics of the country’s volcanoes, while maintaining a watchful eye for signs of unrest.
The stratovolcanoes of Santa Ana and San Miguel have both erupted in the past 25 years, but even more destructive events have occurred in the not-too-distant past. The San Salvador volcano sent a lava flow into presently developed areas in 1917, and Ilopango caldera had a regionally devastating eruption in the year 431.
USGS, through its Volcano Disaster Assistance Program, has maintained a collaborative relationship with the Ministerio de Medio Ambiente y Recursos Naturales for decades. Co-funded by the U.S. Department of State, the program has supported numerous technical investigations and monitoring projects at volcanoes in developing countries around the world.
Meanwhile, many volcanologists in El Salvador have studied in the United States as part of the Center for the Study of Active Volcanoes course held every summer in Hawaiʻi and Washington state.
In recent years, U.S. relationships in El Salvador have focused on geologic projects to describe the eruptive history and hazards of Santa Ana volcano and a broader effort to assemble a national “volcano atlas,” which will include locations, compositions, and hopefully approximate ages for the more than 200 volcanic vents in the country.
Such knowledge will enable more accurate understanding and delineation of hazards associated with their eruptions, which are both explosive (ash-producing) and effusive (lava flow-producing).
The field work in March served both projects. Dozens of samples were collected to correlate and date eruptive deposits across Santa Ana, including three sediment cores from coastal mangroves and a montane bog that may contain distant ashfall from the volcano. Reconnaissance visits were also made to several monogenetic (single-eruption) vents scattered around western El Salvador to assess their genesis and ages.
Finally, the Volcano Disaster Assistance Program sponsored a week-long workshop on lava flow hazards and monitoring for El Salvador staff and partner agencies who have never responded to such an event since the country’s last lava flow was in 1917.
USGS scientists from the Hawaiian, Cascades and Alaska Volcano Observatories discussed their experiences and best practices developed during recent eruptions at Kīlauea and Mauna Loa in Hawaiʻi, as well as Great Sitkin and Pavlof in Alaska.
While the USGS scientists learned plenty about volcanism in El Salvador during this trip, it also provided key insights to bring home to our own volcanoes.
Explosive eruptions in Hawaiʻi are relatively rare, but the ability to correctly interpret their deposits is critical to understanding potential future hazards. Additionally, the more distributed nature of volcanoes in El Salvador has led to interesting interactions between lava flows and their more-weathered depositional environments, not unlike some of Hawaiʻi’s older volcanoes: Hualālai, Maunakea and Haleakalā.
Editorsʻs Note: Volcano Watch is a weekly article and activity update written by scientists and affiliates with the U.S. Geological Survey’s Hawaiian Volcano Observatory .
