35 km either side of the Pacific-Cocos spreading axis at 846'N, on crust 0.6 x 10SUP-6 years old, a pair of small seamounts rises 1.4 km above the faulted terrain of young abyssal hills. A high-resolution traverse made with the sonars and cameras of a deeply towed vehicle shows that the seamounts are inactive volcanoes, with concave side slopes that steepen upwards to 30, and then abruptly flatten at 2-4 km wide summits. Ledges of pillow basalt outcrop on the lower slopes, and form some talus slopes, but the superficial rock of the upper slopes appear to be mainly hyaloclastite. A transponder-navigated deep-tow survey at the summit area of the eastern seamount mapped an asymmetric caldera containing 3 pit craters, which have vertical walls and flat floors. Dredging across the caldera floor recovered hyaloclastite, angular fragments of primitive tholeiite, and manganese nodules. The paired seamounts probably had a common origin at a 'hot spot' on the spreading axis; continued to grow after they were split by sea-floor spreading; and became extinct and suffered summit collapse after they spread too far from their magma source.

From 1983 until 1989 NOAA-NCEI compiled the NOAA-MMS Marine Minerals Geochemical Database from journal articles, technical reports and unpublished sources from other institutions. At the time it was the most extended data compilation on ferromanganese deposits world wide. Initially published in a proprietary format incompatible with present day standards it was jointly decided by AWI and NOAA to transcribe this legacy data into PANGAEA. This transfer is augmented by a careful checking of the original sources when available and the encoding of ancillary information (sample description, method of analysis...) not present in the NOAA-MMS database.

Supplement to: Lonsdale, Peter; Spiess, Fred N (1979): A pair of young cratered volcanoes on the East Pacific Rise. The Journal of Geology, 87(2), 157-173