Mantle updrafts and mechanisms of oceanic volcanism.

Convection in an isolated planet is characterized by narrow downwellings and broad updrafts--consequences of Archimedes' principle, the cooling required by the second law of thermodynamics, and the effect of compression on material properties. A mature cooling planet with a conductive low-viscosity core develops a thick insulating surface boundary layer with a thermal maximum, a subadiabatic interior, and a cooling highly conductive but thin boundary layer above the core. Parts of the surface layer sink into the interior, displacing older, colder material, which is entrained by spreading ridges.

Evidence for mantle plumes?

Geophysical hotspots have been attributed to partially molten asthenosphere, fertile blobs, small-scale convection and upwellings driven by core heat. Most are short-lived or too close together to be deeply seated, and do not have anomalous heat flow or temperature; many are related to tectonic features. Bourdon et al.

Galapagos hydrothermal mounds: stratigraphy and chemistry revealed by deep-sea drilling.

The Galápagos mounds sea-floor hydrothermal system is at least 300,000 years old and once produced manganese-poor sediments, which nearly blanketed the area of the present mounds field. Present-day mound deposits are limited manganese-rich exposures, suggesting that the system has changed from rock-to water-dominated and has diminished in intensity with time.

Cretaceous drowning of reefs on mid-pacific and Japanese guyots.

Reefs dredged on guyots of the Mid-Pacific Mountains and the Japanese Seamounts yield middle Cretaceous fossils, indicating that submergence killed off the fauna of the reefs sometime during the Albian-Cenomanian. Eustatic rise of sea level is probably responsible.