Seamount morphology in the Bowie and Cobb hot spot trails, Gulf of Alaska

Abstract

[1] Full-coverage multibeam bathymetric mapping of twelve seamounts in the Gulf of Alaska reveals that they are characterized by flat-topped summits (rarely with summit craters) and by terraced, or step-bench, flanks. These summit plateaus contain relict volcanic features (e.g., flow levees, late-stage cones, and collapse craters) and as such must have been constructed by volcanic processes such as lava ponding above a central vent, rather than by erosion above sea level. The terraced flanks are composed of a sequence of stacked lava deltas and cones, probably tube-fed from a central lava pond, a morphology which is suggestive of long-lived, stable central lava sources and low to moderate eruption rates, indicative of significant time spent above a hot spot outlet. Most of these seamounts have summit plateaus surrounded, and cut into, by amphitheater headwall scarps, and flanks that are scarred by debris chutes, but lack visible debris accumulations at their base. We interpret the lack of blocky debris fields as evidence that the slope failures are mainly small-scale debris flows, rather than large-scale flank collapses. However, we cannot rule out the possibility that large flank-collapse blocks from early in the histories of these seamounts are now hidden beneath the thick glacio-fluvial fan deposits that cover the Gulf of Alaska seafloor. These slope failure features become smoother and longer and increase in size and abundance with increasing age of a seamount, suggesting that slope failure processes continue long after volcanic activity ceases.

The Structure and Distribution of Benthic Communities on a Shallow Seamount (Cobb Seamount, Northeast Pacific Ocean)

“…It is located in the southward-flowing California Current but experiences a mean clockwise flow with evidence of a Taylor Proudman cap [14, 23]. Over the millennia since its formation, this guyot (flat-topped seamount) has been subject to significant sea-level changes, which, at times, caused it to be subaerial [10–12, 24, 25]. The subsidence history is still evident in the submarine ancient beaches, wave-cut terraces (at approximately 80, 150, 180, and 900 m depth), the eroded basalt pinnacle, and asymmetrical posteruptive slope modifications [10, 12].…”

“…Over the millennia since its formation, this guyot (flat-topped seamount) has been subject to significant sea-level changes, which, at times, caused it to be subaerial [10–12, 24, 25]. The subsidence history is still evident in the submarine ancient beaches, wave-cut terraces (at approximately 80, 150, 180, and 900 m depth), the eroded basalt pinnacle, and asymmetrical posteruptive slope modifications [10, 12]. The combination of volcanic, subaerial, intertidal, and submarine processes has created a mosaic of geological features on Cobb Seamount that provide a diversity of habitats for benthic organisms.…”

“…Since its discovery in 1950, during an exploratory fishing program 500 km off the coast of Washington state, United States of America [8], Cobb Seamount has been the site of many oceanic expeditions (Fig 1). Research on this unusually shallow Northeast Pacific seamount has detailed its geology and geomorphology [9–12], oceanography [13, 14], fisheries [15, 16], and benthic ecology [17, 18] (summit depth: 24 m [18]). Cobb Seamount is regarded as a biological oasis amid the abyss, and is an important international fishing ground and a site for biodiversity conservation [12, 19].…”

Subduction controls of Hf and Nd isotopes in lavas of the Aleutian island arc

“…4) indicate that seamount subduction may also have an effect on the Hf and Nd isotope compositions of Aleutian lavas. The most likely place for seamount subduction in the Aleutian-Alaska system is east of Cold Bay, where clusters of large seamounts in the Gulf of Alaska approach and enter the trench south and southeast of Kodiak Island (figure 1 in Chaytor, et al, 2007). These locations are well east of our eastern-most sample locations, but local bathymetric maps also clearly show a chain of smaller seamounts southeast of Cold Bay, beginning with Derickson Seamount, which is located on the outer margin of the trench near DSDP site 183 ( Fig.…”

Shape and Size Complexity of Deep Seafloor Mounds on the Canary Basin (West to Canary Islands, Eastern Atlantic): A DEM-Based Geomorphometric Analysis of Domes and Volcanoes

“…This fact implies that volcanoes grow primarily by increasing their heights, probably connected to a central-controlled source, and later they also start to grow also laterally, in relation to multiple-point sources. This suggests a different style of volcanic growth [64]. In this sense, volcanoes grow vertically up to a critical height, becoming unstable with respect to their base, and secondary destructive processes may affect the edifice geometry.…”