With complete SeaBeam and SeaMARCII bathymetry and nearly complete SeaMARCII side scan coverage of the northern East Pacific Rise and its flanks from 8¿ to 17 ¿N, we characterize the entire population of seamounts on young seafloor (0 to ~2 Ma) formed along this fast spreading center. There are 179 seamounts in this area taller than 200 m, most of which belong to one of 21 seamount chains. These chains are oriented between the relative and absolute plate motion directions of the Pacific and Cocos Plates, and most of the larger chains are more voluminous near their centers than near their ends. Several of the seamount chains contain bends in orientation which are not coincident with each other. The two largest seamount chains, at 9¿55'N (Lamont Seamounts) and 15¿40'N, are aligned with portions of the East Pacific Rise crest which are among the shallowest and broader ridge of this area. Overall, the maximum abundance and size of seamounds increase with shallower and broader ridge axes. No near-axis seamounts form on the summit of the axial ridge; nonetheless, within 15 km (~0.3 Ma) of the axis, the abundance of seamounts achieves its overall average.

Observations of the numbers and cumulative volume of seamount edifices versus distance from the axis are consistent with a model where the majority of near-axis seamounts are formed in a narrow zone on crust aged ~0.1--0.3 Ma (5--15 km from the axis), with significant growth in a zone several times wider. Side scan sonar reflectivity and seamount magnetization analyses are largely consistent with the predictions of this model. Two exceptions to this model, however, are seamount chains at 15¿40'N and 8¿25'N which show evidence for activity over a broader region; this may be due to the presence of fracture zones within about 30 km of these chains. A compilation of seamount counts from a wide range of spreading centers indicates that seamounts taller than 400 m are more abundant at greater spreading rates and with transitions from a rift valley to an axial ridge. The variations with spreading rate of melt availability and of lithosphere penetrability probably combine to produce the observed results, although these influences cannot be distinguished in this analysis. ¿ American Geophysical Union 1995