Seguam (United States): Recorded Eruptions and Historical Activity

Seguam is a stratovolcano complex located in the United States with an elevation of 1,054 meters. Situated in a subduction zone setting with intermediate crust measuring 15 to 25 kilometers thick, the volcano has a recorded history spanning 11 confirmed eruptions. According to official records from the Smithsonian Global Volcanism Program, these events range from ancient activity dated via isotopic methods to historical eyewitness reports, with the largest recorded event reaching a Volcanic Explosivity Index (VEI) of 5.0.

Overview of Recorded Eruptions

The historical and geological record for Seguam encompasses 11 confirmed eruptions. The earliest recorded activity occurred around 7300 BCE at the Wilcox volcano area, estimated through Ar/Ar isotopic dating with a start-year uncertainty of 2,250 years. Another early event is documented around 4050 BCE on the western flank of the cone in the eastern caldera, determined via Uranium-series isotopic dating with an uncertainty of 4,000 years.

Centuries later, activity shifted into the historical era with eyewitness reports and observations. Confirmed eruptions have been distributed across various centuries, including the 3rd century CE, the 18th century CE, the 19th century CE, and the 20th century CE. For example, an eruption was reported on December 16, 1891, with a VEI of 2.0.

Recent Historical Activity

In the 20th century, activity included eruptions near Pyre Peak, located about 2.5 kilometers southeast of the summit. A reported eruption occurred from March 6 to March 8, 1977, reaching a VEI of 1.0. A later eruption sequence near Pyre Peak began on May 28, 1993, and continued until August 31, 1993, registering a VEI of 2.0.

The profile's last known eruption year is recorded as 1993, corresponding to the start date of the May 28, 1993 event. Official records do not indicate any continuing activity or ongoing eruptions at the volcano.