ALIA Expedition
Nafanua -- A New Volcanic Cone in the Vailulu'u Crater

With a minimum rate of eight inches per day, a new volcanic cone has been growing inside the crater of Vailulu'u seamount since the last depth soundings by the US Coastguard vessel Polar Sea in April 2001. Our survey using the SIMRAD 120 system of the Kilo Moana show a radially symmetric volcanic cone in the eastern portion of the crater that displays a new volcanic summit at 708 m depth. This summit formed in a location of the crater that showed 1000m depth before the new volcano formed. This volcano was named Nafanua, after the Samoan Goddess of War.

2001 - Before	2005 - After
3D Animation of Vailulu'u [ 7.0 MB ] 3D Animation of Growing Nafanua Cone [ 7.0 MB ] 3D Animation of Nafanua Cone [ 3.6 MB ] Before, After and Difference Map Multibeam Map of Vailulu'u Seamount [ pdf ] Multibeam Map of Vailulu'u Crater [ pdf ] Multibeam Map of American Samoa [ pdf ]

Nafanua was discovered during a recent diving expedition with the NOAA research submersible Pisces V launched from the University of Hawaii Research vessel Kaimikai O Kanaloa (KOK). Nafanuas’ active hydrothermal system was apparent from the murky water that limited visibility during two submersible dives, several centimeter thick microbial biomats covering pillow lavas, and a large number of diffuse vents. The ALIA expedition mapped Nafanua and recovered a rock dredge with substantial amounts of pristine olivine-phyric volcanic rocks. Abundant large vesicles in the rocks from Nafanua suggest a volatile-rich magma that is quite capable of submarine lava fountaining and explosive outgassing in shallower water.

Growth rates of Nafanua are sufficiently high to easily fill up the crater of Vailulu’u and bring its summit from its current 600m depth to about 200m within a decade or so. Eruptions of such a shallow volcano could offer substantial hazards to navigation and coastal communities, and involve the risk of tsunamis from potential volcano collapses. While we consider this scenario as very unlikely, it is prudent to keep an eye on this very active volcano.

Hubert Staudigel and Stan Hart onboard the R/V Kilo Moana.
16 April, 2005