he Vance Seamounts comprise the southernmost of several near-ridge chains located on the Pacific Plate near the Juan de Fuca Ridge. No symmetrical seamount chain occurs on the Juan de Fuca Plate. The eastern five of seven volcanoes were previously surveyed using SeaBeam (Hammond, 1997). The few chemical analyses of lavas that have been published are relatively primitive, depleted N-MORB (Smith et al.,1994).
Six of the seven volcanoes form a roughly linear array of cones that are nearly circular in plan view. The second volcano from the northwest is not a discrete cone like the rest, but rather a region of rough, elevated seafloor consisting of lava cones and flows, covering an area at least 25 by 10 kilometers. The six conical volcanoes have an average volume of 34±15 km3 with a range of 15 to 67 km3. Most of their gently-domed summit plateaus have been modified by the collapse of nested calderas (11 in total) that appear to step down to the southeast. Several of the volcanoes also have low shield volcanoes on their summits, commonly modified by calderas. Some calderas are very shallow, having been flooded and filled almost completely by subsequent flows, preserving only portions of their rims. Some calderas have hummocky landslide deposits on the nearly flat floors near the base of the steep caldera walls. The nearly flat tops of several of the volcanoes slope gently down to the southeast and several of the calderas are breached on the southeast side. Small cones and shields dot the seafloor around some of the volcanoes. Ridge-parallel faults cut the summit platforms of several of the southeastern volcanoes. These faults have only low relief—on the order of a few tens of meters—and do not step systematically down to the southeast.
The constructional volcanic region consists of high-backscatter material, presumably lava that forms a broad 700-meter-high rise with superposed roughness. Much of the roughness can be resolved into individual cones, some with summit craters, and small volcanic ridges aligned parallel to the ridge axis. The largest of the cones is nearly 2 kilometers across and the smallest appear to be only a few hundred meters across. The volume of the dome and cones (67 km3) is roughly equivalent to any two of the circular volcanoes in the Vance chain, but the volcanic activity was less centralized.
Clague et.al. (2000) discuss the volcanic propagation rates and orientation of the chain relative to plate motion, and examines the magmatic history based on the morphological data.
|Index Map||Axial Volcano||Gorda Ridge||Cleft Segment||Taney Seamounts|
|Guide, Gumdrop, Pioneer Seamounts||Mendocino Fracture Zone||President Jackson Seamount||Davidson Seamount||Vance Seamounts|