Multibeam Studies of Abyssal Hills on the Flanks of the East Pacific Rise ISS, 10\deg18'N to 10\deg50'N.

We have acquired multibeam data for the East Pacific Rise (EPR) and its flanks from 10\deg18'N to 10\deg50'N, a segment of the EPR ISS zone. We are exploiting that data to characterize abyssal hill topography generated over a segment of ridge whose morphology changes rapidly along its length. Combined sets of bathymetric data from two cruises, in 1994 and 2003, cover an area of approximately 7000 km² to the north of the Clipperton Fracture Zone (CFZ). Adjacent the CFZ, the ridge axis is nearly indistinguishable from the surrounding seafloor, and lacks the axial high characteristic of mid-ocean ridges with a steady state magma chamber. As the ridge continues north, it becomes shallower, broader and more defined. The subdued topography to the south, along with the lack of an apparent axial magma chamber reflection (Detrick et al., 1987), has led many to argue that the ridge axis from 10\deg18'N to 10\deg55'N has a depleted magma supply. This reasoning implies that the magma supply increases northward along the ridge axis, corresponding to a change in the thermal structure. This variation in thermal structure may result in changes in the physical characteristics of abyssal hill topography. For example, at a ridge segment with an abundant magma supply, the warmer (thinner) lithosphere is likely to result in more closely spaced abyssal hills. These bathymetric data allow us to examine the influence of magmatic budget and thermal structure on the formation and distribution of abyssal hills along a fast-spreading ridge. We investigate how the varying ridge morphology affects the off-axis topography by measuring the spacing, distribution, rms height, and length of abyssal hills. Preliminary analysis of three transects across the field area at 10\deg25'N, 10\deg30'N and 10\deg40'N show that there is no obvious or consistent trend to the spacing of abyssal hill faults, particularly east of the ridge axis. There is a region of generally higher bathymetry at ∼104\deg00'W that is not mirrored on the east side of the ridge. This area of high bathymetry corresponds to larger and less regular spacing between scarps. Fault spacing averages 3.31 km over all transects, and varies between 2.36 and 4.80 km.