"Sister Peak" (Comfortless Cove Hydrothermal Field, , elevation −2996 m), "Shrimp Farm" and "Mephisto" (Red Lion Hydrothermal Field, , elevation −3047 m), are three hydrothermal vents of the black smoker category, on the Mid-Atlantic Ridge near Ascension Island. They are presumed to have been active since an earthquake shook the region in 2002. These vents have been observed to vent phase-separated, vapor-type fluids. In 2008, sustained exit temperatures of up to 407 °C were recorded at one of these vents, with a peak recorded temperature of up to 464 °C. These thermodynamic conditions exceed the critical point of seawater, and are the highest temperatures recorded to date from the seafloor. This is the first reported evidence for direct magmatic-hydrothermal interaction on a slow-spreading mid-ocean ridge. The initial stages of a vent chimney begin with the deposition of the mineral anhydrite. Sulfides of copper, iron, and zinc then precipitate in the chimney gaps, making it less porous over the course of time. Vent growths on the order of 30 cm (1 ft) per day have been recorded. An April 2007 exploration of the deep-sea vents off the coast of Fiji found those vents to be a significant source of dissolved iron (see iron cycle).