Davidson Seamount - Geology

Geology

A seamount such as Davidson is an underwater volcano; this one rises over 3,280 ft (1,000 m) above the surrounding ocean floor. Although there are over 30,000 seamounts in the Pacific Ocean alone, only about 0.1% of them have been explored. The aqueous environment of the seamount means that it behaves differently to volcanoes on land. Its surface is composed mostly of blocky lava flows, although some pillow lava, which is the typical lava type of a seamount, prevails at the deeper flank. The summit is composed of layered deposits of volcanic ash and pyroclastic material. These rocks indicate mildly explosive eruptions of gas-rich lava near the summit of the volcano. The base of Davidson is probably buried in a deep layer of muds.

At 26 mi (42 km) long and 8 mi (13 km) wide, Davidson Seamount is impressively large. If it were on land, it would dominate the landscape in a way similar to how Mount Shasta dominates the horizon of northern California. Put in perspective, the size of the seamount is enough to fill Monterey Bay from the Santa Cruz boardwalk to Monterey's Fishermen's Wharf.

Davidson Seamount is part of a group of seamounts off the continental margin, including Guide, Pioneer, Gumdrop, and Rodriguez seamounts, all located roughly between 37.5° and 34.0° degrees of latitude. This group is morphologically unique, and very similar to one another. All the seamounts in the group are complex northeast-southwest trending structures, consisting of parallel ridges separated by sediment-filled troughs. The ridges constructed run parallel to an ancient spreading center which has since been replaced in its role by the San Andreas Fault system. They are unique in this origin, as they are formed from the remnants of an old ocean-ridge spreading center. A series of "knobs" are aligned with the ridges; however the distinctive summit crater, evident in many oceanic volcanoes, is absent. This lack of a collapse crater suggests that magma was never stored in a chamber within the structure, as with most other volcanoes.

Analysis of argon–argon dating studies indicate that Davidson formed between 9 and 15 million years ago, 5 to 12 million years after the formation of the overlaying oceanic crust.