Redoubt (United States): Recorded Eruptions and Historical Activity

Redoubt is a stratovolcano located in the United States, positioned within a subduction zone on continental crust thicker than 25 kilometers. Rising to an elevation of 3,108 meters at latitude 60.485 and longitude -152.742, the volcano has a documented history featuring 97 confirmed eruptions recorded in the Smithsonian Global Volcanism Program database.

Geological Setting and Eruption Overview

As a stratovolcano—a tall, conical mountain built up of alternating layers of hardened lava, tephra, pumice, and volcanic ash—Redoubt sits in an active tectonic environment where one tectonic plate slides beneath another. The historical record for the volcano encompasses 97 confirmed eruptions stretching across millennia. Scientific methods used to establish this timeline range from sidereal varve counting for ancient events to direct human observations for modern activity.

Across the entire recorded history, the largest confirmed eruptions reached a Volcanic Explosivity Index (VEI) of 3.0. The VEI scale provides a relative measure of the explosiveness of volcanic eruptions based on factors such as volume of products ejected and eruption cloud height. Out of the 97 confirmed eruptions, 6 include recorded VEI observations.

Chronology of Historical Activity

The earliest recorded eruption in the official database dates back to 9310 BCE, determined through sidereal varve counting methods with an estimated start year uncertainty of 300 years. Ancient activity continued intermittently through various centuries BCE and CE, captured through geological proxy methods such as sediment layer analysis (varves) before transitioning into direct historical accounts.

Representative milestones in the eruption timeline illustrate the long-term behavior of the volcano:

• 9310 BCE: Early recorded activity identified via varve count (uncertainty of 300 years).
• 3690 BCE: Confirmed eruption identified via varve count (uncertainty of 150 years).
• 1100 BCE: Confirmed eruption identified via varve count (uncertainty of 100 years).
• 90 BCE: Confirmed eruption identified via varve count (uncertainty of 75 years).
• March 15, 2009 – July 1, 2009: A confirmed eruption with a recorded VEI of 3.0, taking place south of the 1990 dome, documented through reported observations.

The latest confirmed eruption event concluded on July 1, 2009, following its start on March 15, 2009. The profile's last known eruption year is recorded as 2009.