Terceira is a stratovolcanic system located in Portugal, positioned along a rift zone in oceanic crust less than 15 kilometers deep. Reaching an elevation of 1,023 meters, the volcano has a recorded history of 15 confirmed eruptions spanning thousands of years, with activity ranging from early uncalibrated radiocarbon-dated events to historical, direct observations.
Geological Overview and Activity Record
The Smithsonian Global Volcanism Program records 15 confirmed eruptions for Terceira. The earliest recorded eruption in the collection dates back to approximately 6720 BCE in the Guilherme Moniz (Pico das Pardelas) area, with a start year uncertainty of 50 years. Over subsequent millennia, activity occurred across various vents, fissure zones, and submarine areas associated with the volcanic complex.
The eruption timeline encompasses multiple centuries across both BCE and CE eras:
- 68th century BCE: 1 confirmed eruption (starting around 6720 BCE)
- 26th century BCE: 1 confirmed eruption
- 10th century BCE: 1 confirmed eruption
- 7th century BCE: 1 confirmed eruption
- 1st century BCE: 2 confirmed eruptions (including an activity area east of Santa Barbara starting around 90 BCE with a 100-year uncertainty)
- 1st century CE: 1 confirmed eruption
- 2nd century CE: 1 confirmed eruption (such as Guilherme Moniz [Pico Alto] starting around 0190 CE with a 40-year uncertainty)
- 9th century CE: 1 confirmed eruption
- 10th century CE: 1 confirmed eruption
- 12th century CE: 1 confirmed eruption
- 14th century CE: 1 confirmed eruption
- 18th century CE: 1 confirmed eruption
- 19th century CE: 1 confirmed eruption
- 20th century CE: 1 confirmed eruption
Historical and Submarine Eruptions
As observational methods improved, historical reporting captured more precise dates for submarine and vent activity around Terceira. For example, a confirmed eruption occurred at a submarine vent 3 to 6 kilometers west-northwest of Terceira, lasting from June 1, 1867, to June 8, 1867. This event reached a Volcanic Explosivity Index (VEI) of 3.0, which stands as the largest recorded VEI in the available dataset.
More recently, activity was documented along the Serreta Ridge, a submarine vent west of Terceira. This eruption began on November 25, 1998, and concluded on March 16, 2000, with a recorded VEI of 0.0. In the structured profile records, the latest structured eruption start is listed as November 25, 1998, while the profile's last-known eruption year is referenced as 2000.
Frequently asked questions
How many eruptions have been recorded at Terceira?
The Smithsonian Global Volcanism Program records 15 confirmed eruptions for Terceira, stretching from approximately 6720 BCE to the eruption that concluded in March 2000.
When did the earliest recorded eruption take place?
The earliest recorded eruption in the official dataset began around 6720 BCE in the Guilherme Moniz (Pico das Pardelas) area, with a start year uncertainty of 50 years.
What is the largest recorded VEI for Terceira?
The largest recorded Volcanic Explosivity Index (VEI) for Terceira is 3.0, which was measured during the June 1867 submarine eruption.
Sources and further context
Official datasets support the event-specific facts.