Eifuku () and NW Eifuku () are two seamounts in the Pacific Ocean. The better known one is NW Eifuku, where an unusual hydrothermal vent called "Champagne" produced droplets of liquid . Both seamounts are located in the Northern Marianas and are volcanoes, part of the Izu-Bonin-Mariana Arc. NW Eifuku rises to depth below sea level and is a wide volcanic cone.
Both Eifuku seamounts are hydrothermally active, with numerous vent sites found on NW Eifuku including the "Champagne" vent site, where there are a number of white smokers. Diverse ecosystems dominated by mussels live in proximity and around the hydrothermal vent sites.
Geography and geology
The Eifuku seamounts are located northwest of Farallon de Pajaros island in the Northern Marianas. Geologically, both Eifuku seamounts are part of the Northern Marianas volcanic arc and are grouped within the Northern Seamount Province. The Northern Marianas are part of the Izu-Bonin-Mariana Arc between Japan and Guam, which owes its existence to the subduction of the Pacific Plate underneath the Philippine Plate that began in the Eocene. About 40 submarine and island volcanoes make up the Northern Marianas arc.
NW Eifuku and Eifuku are small volcanoes at the northwestern end of a volcano chain that also includes Daikoku, which is larger than NW Eifuku. Daikoku also features hydrothermal venting and has been considered a twin cone with Eifuku. Eifuku proper is composed of boulders, dykes and lava domes. The occurrence of volcanic breccia, hydrothermal muds, sandstone and sulfides has been reported but without a clear attribution to either Eifuku or NW Eifuku.
NW Eifuku seamount rises to depth below sea level and has a roughly conical outline, with a basal width of . Its summit is formed by a lava dome that is surrounded by jagged rocks. A ridge, which likely corresponds to a dyke in the crater, runs from the summit and features old and mostly inactive hydrothermal vents. Rocks with columnar joints, lava spines and pillow basalts are found in the summit region. The southwestern slope of NW Eifuku and its summit are cut by the scar of a sector collapse. A northwest-southeast trending fracture may underlie the seamount and could be responsible for the mass wasting observed on the seamount. The venting at "Champagne" appears to indicate that there is degassing magma.
Composition
Rocks erupted by Eifuku range from basalt to andesite that define either a potassium-rich calc-alkaline or a tholeiitic suite. The basalts contain clinopyroxene, olivine and plagioclase and feature abundant vesicles despite the great depth of the volcano. This composition may occur on either NW Eifuku or Eifuku or both seamounts. Sulfur mineralizations exist in the form of crusts, large deposits and also as infill within other rocks. Silica and iron oxides form fluffy sediments.
Hydrothermal vents
Both Eifuku and NW Eifuku are hydrothermally active, with NW Eifuku displaying white smokers and hydrothermal vents dispersed over several sites on the volcano. There are several sites, including diffuse venting at the summit, a low-temperature area at depth and high-temperature vents at depth which include the so-called "Champagne" site about west-northwest of the summit. Two other vent sites northeast and north of "Champagne" are known as "Cliff House" and "Sulfur Dendrite", respectively. Additional vents are "Yellow Cone" and "Yellow Top" which are low-temperature iron-rich vents and the latter of which is located south of the summit. A sixth vent site is known as "Bacto Balls". The seawater above NW Eifuku has anomalous composition, a sign of hydrothermal degassing.
Champagne vent
The "Champagne" vent was discovered either in 2004 by the ROPOS remotely operated vehicle (ROV) or by a NOAA expedition in 2003. It lies west of the summit in the sector collapse scar and features both focused (white smokers that form chimneys) and diffuse venting. Temperatures of the discharge reach in gas-rich fluids that contain . The chimneys are formed by sulfur.
"Champagne" is known for being one of only two sites on Earth where liquid is emitted. The rises from the pumice and sulfur deposits on the ground through crevices, and it forms cold droplets with a milky skin that stick to surfaces such as ROV tools and ascend slowly owing to their buoyancy under the conditions at the vent. They appear to originate from a layer underneath the ground surface, as disturbing it leads to increasing exhalations. The name "Champagne" is based on the appearance of the exhalations.