Which ridge is spreading faster

Why does the mid-ocean ridge crest have such variable topography? This is an important question that marine geologists and geophysicists are studying. Part of the research we are doing is to answer this question. Menard, H. Morton, J. Nisbet, E. Normark, W. Orcutt, J. Pallister, J. Parker, R. Poehls, K. Prothero, W.

Geon ys. Purdy, G. Ramberg, I. Riedesel, M. Reid, I. Rona, P. London , — Rosendahl, B. A physical model of the East Pacific Rise crest derived from seismic refraction data, J. Schouten, H. Earth Planet Sci. Sclater, J. Simoneit, B. Sleep, N. Rona et al. Centers , Plenum, in press. Stakes, D. Talwani, M. Tapponnier, P. Toomey, D. Trehu, A. Turekian, K. Van Andel, T. Watts, A.

Palmason, ed. Whitmarsh, R. Williams, D. Woodside, J. Earth Sci. Young, P. In contrast with slow spreading mid-ocean-ridges, where hundreds of seamounts form in the rift along the crest or the ridge, volcanism at fast spreading mid-ocean-ridges is much like the subaerial fissure erupts associated with volcanic rift zones.

This photo shows a curtain of fire during an eruption of Mauna Loa in Hawaii. Photo by Robin Holcomb, U. The thick black lines show the location of the spreading axes along the rise.

The thick red lines indicate portions of the rises where the presence of an axial magma chamber has been inferred. Stars show the location of active hydrothermal vent areas.

Compare to the computer-generated topographic map at the top of this page. Modified from Macdonald and Fox Magma chambers extend tens of kilometers along the axes of fast spreading mid-ocean-ridges. These magma chambers feed the fissure eruptions. Some magma chambers are only little more than half a mile one kilometer beneath the seafloor. This cross-section of the oceanic crust along the northern East Pacific Rise is based on a model proposed by Sinton and Detrick and modified by Perfit and others The cross-section is 5 miles 8 km across and 3 miles 5 km deep.

The 'Moho' marks the base of the crust and the top of the mantle. In addition to fissure eruptions, another style of volcanism occurs at fast-spreading mid-ocean ridges. Central-vent eruptions away from the axis of the spreading center form near-axis seamounts Scheirer and Macdonald, These volcanoes range in height from , feet m. Small seamounts are much more common than large ones with the characteristic height of seamounts in the Pacific ranging from feet m.