The Taney Seamounts are located on the Pacific Plate, west of San Francisco. It is unknown whether a symmetrical chain of volcanoes existed on the subducted Farallon Plate. GLORIA imagery (Geological Long-Range Inclined Asdic, EEZ-Scan 84 Scientific Staff, 1986, 1988) shows that the chain does not extend beyond the region that we have imaged. The Taney Seamounts were incorrectly inferred to be young volcanoes based on their morphology (EEZ-Scan 1984 Scientific Staff, 1988). However, an Ar-Ar age of approximately 26 million years for volcano T-A (G.B. Dalrymple, cited in Davis et al., 1998) demonstrates that their age is close to that of the underlying seafloor. Dredges on the northwestern volcano in the chain have recovered E-MORB and mildly alkalic pillow basalts (Davis et al., 1998), and MBARI has recently done ROV dives on two of the volcanoes. The following descriptions are summarized from Clague et al. (2000), who analyzed the Simrad data presented here in detail.
The Taney Seamounts consist of five aligned volcanoes. The volcanoes have an average volume of 86±64 km3, range 11 to 187 km3. The northwestern volcano is by far the largest volcano in the chain, with a calculated volume of 187 km3. The volcano has been so severely modified by three successive caldera collapses that most of the summit platform has been destroyed. The southeastern portion of the floor of the third and southeastern caldera has been modified by eruptions that formed many 0.5-1.0 kilometer diameter cones and several roughly 1-kilometer diameter low, flat-topped shields. The large embayment north of the southeastern caldera may be caused by a landslide or by faulting along a ridge-parallel fault.
The summit of the next volcano to the southeast is an unusual large caldera, about 6.5 by 4.5 kilometers. The volcano is oval, with the long axis parallel to the chain. The rim of the large caldera varies in height up to about 150 meters tall. The east-southeastern rim has been overtopped by lava flows erupted within the caldera that flowed from the floor down the flank, and then ponded at the base of the slope to form a lava delta. A small step on the southern flank of the volcano, seen as an illuminated band about halfway up the flank, may be a somma—the rim of an even earlier, and larger, caldera that was almost entirely filled by a subsequent shield. The next volcano to the southeast has three oval calderas with their long dimension parallel to the chain. The southeastern caldera dropped the southeastern rim of the summit by about 575 meters. The eastern rim of the summit platform is scalloped, apparently by several landslides. A pit crater in the northwestern part of the flat summit of the fourth volcano from the northwest is less than 100 meters across and about 60 meters deep. Unlike the other 13 calderas, this is the only collapse feature in the Taney Seamounts that is less than 1.5 kilometers in diameter.
|Index Map||Axial Volcano||Gorda Ridge||Cleft Segment||Taney Seamounts|
|Guide, Gumdrop, Pioneer Seamounts||Mendocino Fracture Zone||President Jackson Seamount||Davidson Seamount||Vance Seamounts|