MAR 26°04'N 



KM 



AXIS 



5KM 



Figure 4. Bathymetric profiles of slow- (full rate <^ 4 cm/y; 



Mid-Atlantic Ridge [MAR], 26°04'N), intermediate- (full rate 

 > 4-8 cm/y; Gorda Ridge [GR] , 42°45'N; East Pacific Rise 

 [EPR] 21°N), and fast- (full--rate > 8 cm/y East Pacific 

 Rise [EPR], 3°25'S) spreading oceanic ridges. Topographic 

 relief decreases with increase of spreading rate (Fig. 1). 

 An axial zone of volcanic extrusion ( ~ 1 km wide) is bounded 

 by marginal zones of active extension (~ 10 km wide). 

 Vertical exaggeration is 4:1. 



12 



