Wavelet-Based Analysis of Constructional Features on the Flanks of the East Pacific Rise, 10deg18'N to 10deg50'N

The morphology of the East Pacific Rise (EPR) from 10°18'N to 10°50'N changes rapidly from south to north. At the southern end of the segment, adjacent to the Clipperton Transform, the ridge axis is deep and narrow, and becomes broad and shallow to the north. These changes have been attributed to variations in thermal structure, and therefore to the magma supply, of the mid-ocean ridge. Because the thermal structure has a large influence on the formation of oceanic crust, we expect to see corresponding changes in constructional features such as volcanic cones and abyssal hills. Within the study area, abyssal hills are common, but there is only one major seamount. Many smaller volcanic cones exist, but are often difficult to identify do to larger-scale variations in topography. In order to identify and quantify features such as small volcanic cones and abyssal hills, we have designed and employed wavelet-based filters that enhance the signal from desired geomorphic features, and reduce or eliminate the signal from the remaining bathymetry. We have shown that abyssal hills lack a strong systematic north-south variability in this area. Instead they exhibit irregular distribution patterns, likely related to temporal and spatial changes in the thermal structure of the ridge. We also designed filters that enhance seamounts and reduce the signal from abyssal hills, the ridge axis, and the Clipperton Transform. These filters are based on a two-dimensional Morlet wavelet, but have been modified to remove side lobes and to be flat-topped. They amplify round, flat-topped seamounts well, but irregularly shaped seamounts are more difficult to enhance. This approach is particularly versatile because we can perform multiple passes with filters of different wavelengths, thus characterizing seamounts and volcanic cones by location and size. Preliminary results suggest that volcanic cones, like abyssal hills, are not systematically distributed. Circular filters with wavelengths of approximately 3 km return more peaks than do filters of smaller or larger scales. While large seamounts may indicate a steady magma supply, the abundant small seamounts that we see here may imply an intermittent magma supply. The analysis of seamount, volcanic cone, and abyssal hill distributions allows a more complete characterization of the thermal structure of this rapidly-changing segment of the East Pacific Rise.