Seamounts

Abstract

DefinitionSeamounts are literally mountains rising from the seafloor. More specifically, they are "any geographically isolated topographic feature on the seafloor taller than 100 m, including ones whose summit regions may temporarily emerge above sea level, but not including features that are located on continental shelves or that are part of other major landmasses" . The term "guyot" can be used for seamounts having a truncated cone shape with a flat summit produced by erosion at sea level (Hess, 1946), development of carbonate reefs (e.g., Flood, 1999), or partial collapse due to caldera formation (e.g., Batiza et al., 1984). Seamounts <1,000 m tall are sometimes referred to as "knolls" (e.g., Hirano et al., 2008). "Petit spots" are a newly discovered subset of sea knolls confined to the bulge of subducting oceanic plates of oceanic plates seaward of deep-sea trenches (Hirano et al., 2006). Charting, Abundance, and DistributionSeamounts form one of the most common bathymetric features on the seafloor. Two techniques, both with advantages and disadvantages, have been used to chart them. The first technique is satellite altimetry that measures the height between a satellite and the instantaneous sea surface. This distance can be used after correction for oceanographic effects on the sea surface to derive the geoid undulation, which (with assumptions) can be used to derive gravity anomalies. These are then converted (with assumptions) to seafloor bathymetry (Wessel, 2001). This technique permits full coverage of the ocean floor in the 72° latitude range. However, oceanographic noise at the sea surface limits the identification of seamounts smaller than ~1.5 km in most areas of the ocean (Wessel et al., 2010). The second type of technique uses ship SONAR (e.g., multibeam echo-sounding systems) or towed/autonomous underwater vehicles (AUVs), allowing topographic mapping at high resolution of the ocean floor. This technique permits recognition of seamounts of virtually any size provided that they are not entirely covered by sediment. However, the spatial coverage of the multibeam swath is restricted to a narrow stripe beneath the vehicle conducting the measurements, with the width of the stripe increasing with water depth between the vehicle and the seafloor. As a consequence, <10 % of the global seafloor has been charted using this method. Size-frequency relationship of seamounts based on satellite and ship track data can be combined to estimate the total number of seamounts (Hillier and Watts, 2007). It is therefore speculated that there are 3-80 million seamounts greater than 100 m in height on the seafloor. The total number and global distribution of smaller seamounts, however, remains poorly constrained due to relatively limited coverage of the seafloor by echo sounding. Around 90 % of the seamounts, a fraction primarily including the smallest, <100 m-tall edifices, remain to be charted (Wessel et al., 2010). Only a very limited number of seamounts are currently included in open-source databases like the Seamou...

A Global Survey of Gravitationally Deformed Volcanoes on Venus

“…The Hawaiian–Emperor island/seamount chain is a prime example of intraplate seamounts that form from local melt anomalies or “hotspots” (Buchs et al., 2015). Along the northwest portion of the Hawaiian ridge, just northwest of Neva Shoal, is an unnamed seamount ∼45 km in diameter at its base, and with a height of ∼5 km.…”