Located nearly 300 miles off the coast of Oregon, Axial Seamount is the most active submarine volcano in the northeastern Pacific. It rises to a depth of about 4,600 feet below the ocean’s surface and serves as a premier natural laboratory for studying underwater volcanic activity. Its frequent eruptions and the advanced technology deployed on its summit provide scientists with an opportunity to observe geological processes in real time.
Geological Significance and Location
Axial Seamount is situated on the Juan de Fuca Ridge, a tectonic spreading center where the Juan de Fuca plate and the Pacific plate are pulling apart at a rate of about two inches per year. This ridge is part of the global mid-ocean ridge system, an underwater mountain range where new oceanic crust is formed. The seamount itself is the youngest volcano in the Cobb-Eickelberg Seamount chain, a line of volcanic mountains formed by a geological hotspot that intersects with the ridge. This positioning contributes to its robust magmatic system.
The volcano’s summit is distinguished by a large, rectangular caldera, approximately 1.8 by 5 miles in size. This feature was formed by the collapse of the volcano’s summit following a massive eruption. The caldera is bounded by faults reaching up to 500 feet in height and is flanked by two extensive rift zones that stretch for miles to the northeast and southwest. These rifts are characterized by long fissures in the seafloor from which lava has erupted.
A Cycle of Volcanic Activity
Axial Seamount exhibits a predictable cycle of activity driven by the movement of magma deep beneath the seafloor. Between eruptions, its magma chamber steadily fills, causing the caldera floor to gradually swell upwards in a process known as volcanic inflation. The seafloor can rise by several feet over a period of years as pressure builds in the underlying magma reservoir. This inflation continues until the pressure triggers a new eruption.
During an eruption, magma is expelled from the chamber and erupts as lava onto the seafloor, causing the caldera floor to rapidly subside in a process called deflation. The last eruption in 2015 caused the seafloor to drop by about 8 feet. Since that event, the volcano has been steadily re-inflating, recovering a significant portion of the elevation lost during that eruption.
The pattern of seismic activity also provides clues about impending eruptions. In the months leading up to an eruption, the number of small earthquakes increases as the rising magma stresses the surrounding crust. During an eruption, thousands of earthquakes can be detected as magma moves through underground dikes to the surface. For example, the 1998 eruption began with seismic activity at the summit, which then migrated southward along the rift zone as a dike propagated for miles.
Life Around Hydrothermal Vents
The volcanic heat from Axial Seamount powers ecosystems clustered around hydrothermal vents. Seawater seeps into the ocean crust, where it is heated by the underlying magma. This superheated, mineral-rich fluid then jets back out into the cold ocean through chimney-like structures known as “black smokers.” The “smoke” is a dark plume of iron and sulfur compounds that precipitate out of the hot fluid as it mixes with the near-freezing seawater.
In this environment of total darkness and immense pressure, life is not based on photosynthesis but on chemosynthesis. Specialized microbes, including bacteria and archaea, form the base of the food web by harnessing chemical energy from compounds like hydrogen sulfide released by the vents. These extremophiles convert the inorganic chemicals into organic matter, providing nourishment for a host of unique animals.
The vent communities include species such as giant tubeworms, which have no mouth or digestive tract but host chemosynthetic bacteria within their bodies that produce their nutrition. Other inhabitants include limpets, scale worms, and various microbial mats that cover the seafloor. These biological communities are directly linked to the volcano’s activity, flourishing in the chemical-rich fluids it provides and facing disruption when eruptions pave over existing vent sites with new lava flows.
The Underwater Observatory
Our detailed understanding of Axial Seamount is possible because it hosts an advanced cabled underwater observatory. As part of the National Science Foundation’s Ocean Observatories Initiative (OOI), a high-power electrical and fiber-optic cable runs from Pacific City, Oregon, directly to the volcano’s summit. This Cabled Array provides continuous power and two-way, real-time communication to scientific instruments on the seafloor.
This permanent installation allows scientists to monitor the volcano 24/7, a major improvement over periodic ship-based expeditions. The array includes a network of instruments, such as:
- Seismometers to detect earthquakes
- Pressure and tilt sensors to measure the inflation and deflation of the caldera floor
- Chemical sensors to analyze the fluids from hydrothermal vents
- High-definition cameras to provide visual data on the volcanic and biological activity
The real-time data from the Cabled Array enables eruption forecasting. Scientists can watch the seafloor rise centimetre by centimetre and see earthquake activity increase, providing warnings of an impending event. This information has transformed the study of submarine volcanoes, making Axial Seamount a focal point for research into the processes that shape our planet.