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The 1998 eruption at Axial

A major eruption of Axial Volcano began on January 25th, 1998. The action began with a swarm of earthquakes in Axial Caldera that was detected by hydrophones from the US Navy’s Sound Surveillance System (SOSUS). Within the first day of activity, earthquakes began to migrate southward along the volcano’s south rift zone. This was an indication that magma was moving out from beneath the summit of the volcano and that a dike was intruding into the south rift zone.

A dike is a magma-filled crack that is forced open by magmatic pressure. Dikes are the main way that magma is transported in the Earth’s crust, especially in areas of extension. During most seafloor spreading episodes, dikes intrude between the tectonic plates and incrementally force them apart by about 1-2 meters. During the first two days of activity at Axial, the dike propagated a distance of 50 km from the summit caldera along the south rift zone, sometimes moving as fast as ~1 m/s. Dikes sometimes reach the surface to feed eruptions, but not always and not everywhere along their length. At Axial, the 1998 dike only erupted along the northern 9 km of the south rift zone. The focus of the NeMO Explorer site is at the northern end of the 1998 eruptive area.
Although the earthquake activity continued for 11 days, most of the magma movement occurred in the first few days. During that same time period, a bottom pressure recorder located near the center of Axial’s caldera showed that the caldera floor subsided by a total of 3.2 m. This is another indication that a large volume of magma that had been stored in a reservoir beneath the caldera was removed and intruded into the rift zone. This deformation of the volcano has been used to estimate the depth of that magma reservoir (3.8 km below the caldera floor) and the volume of magma removed during this event (~200 million cubic meters).
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Related video clips:
Animation of 1998 earthquake swarm at Axial

Other NeMO-related concepts:
NeMO at Axial | the 1998 eruption | the rumbleometer story | lava flow animation
Animal Gallery | chemosynthesis | biological colonization of new lava

Mid-ocean ridges | seafloor spreading | seamounts & hot spots | calderas | Axial volcano
Hydrothermal vents | fluid paths | focused vents | diffuse vents | sulfide | anhydrite
Lava morphology | sheets | pillows | lava contacts | skylights | pillars | the 1998 flow

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