Giggenbach, named after volcano gas geochemist Werner Giggenbach, is a basaltic-to-dacitic submarine volcano about 30 km NW of Macauley volcano. The flat summit reaches to within 65 m of the ocean surface, has a 700-m-wide crater containing a central cone, and is cut by numerous small explosion pits and craters. Much of the edifice is covered by dacitic pumice, and several edifice-collapse scarps cut its flanks. Large cones are found on the ENE and SSW flanks, and a chain of eight small cones that fed recent andesitic-dacitic lava flows lies on the west flank. A large hydrothermal vent field was found within the summit crater.