Rodriguez Seamount is a

seamount A seamount is a large geologic landform that rises from the ocean floor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise a ...

and

guyot In marine geology, a guyot (pronounced ), also known as a tablemount, is an isolated underwater volcanic mountain (seamount) with a flat top more than below the surface of the sea. The diameters of these flat summits can exceed .Central California Central California is generally thought of as the middle third of the state, north of Southern California, which includes Los Angeles, and south of Northern California, which includes San Francisco. It includes the northern portion of the San Jo ...

. It is structurally similar to the nearby

Guide A guide is a person who leads travelers, sportspeople, or tourists through unknown or unfamiliar locations. The term can also be applied to a person who leads others to more abstract goals such as knowledge or wisdom. Travel and recreation Exp ...

Pioneer Pioneer commonly refers to a settler who migrates to previously uninhabited or sparsely inhabited land. In the United States pioneer commonly refers to an American pioneer, a person in American history who migrated west to join in settling and dev ...

Gumdrop Gumdrops are a type of gummy candy. They are brightly colored pectin-based pieces, shaped like a narrow dome (sometimes with a flattened top), often coated in granulated sugar and having fruit and spice flavors; the latter are also known as spi ...

, and

Davidson Davidson may refer to: * Davidson (name) * Clan Davidson, a Highland Scottish clan * Davidson Media Group * Davidson Seamount, undersea mountain southwest of Monterey, California, USA * Tyler Davidson Fountain, monument in Cincinnati, Ohio, USA ...

seamounts, all located roughly between 37.5° and 34.0° degrees of

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north po ...

. This group of seamounts is morphologically unique, and the mounts are very similar to one another. The seamount structures run parallel to an ancient

spreading center A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a dive ...

which has since been replaced in its role by the

San Andreas Fault The San Andreas Fault is a continental transform fault that extends roughly through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal) ...

system.

Geology

Magnetic anomalies In geophysics, a magnetic anomaly is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks. Mapping of variation over an area is valuable in detecting structures obscured by overlying ...

at Rodriguez indicate that it is located on a 19-million-year-old crustal surface. Rocks recovered from Rodriguez Seamount are largely composed of

alkaline basalt Alkali basalt or alkali olivine basalt is a dark-colored, porphyritic volcanic rock usually found in oceanic and continental areas associated with volcanic activity, such as oceanic islands, continental rifts and volcanic fields. Alkali basalt ...

and

Hawaiite Hawaiite is an olivine basalt with a composition between alkali basalt and mugearite. It was first used as a name for some lavas found on the island of Hawaii. It occurs during the later stages of volcanic activity on oceanic islands such as Haw ...

. Ar-Ar dating techniques indicate that the volcano is between 10 and 12 million years of age. Rodriguez Seamount rises about above the surrounding seafloor, to a minimum depth of . Its calculated volume is greater than ; however this is likely an understatement because the survey did not include its lowermost slope. The slope is composed mostly of layered

volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcan ...

, mostly coarse sandstone, with a few scattered large lava boulders. They were likely formed from fragments of

volcanic glass Volcanic glass is the amorphous (uncrystallized) product of rapidly cooling magma. Like all types of glass, it is a state of matter intermediate between the closely packed, highly ordered array of a crystal and the highly disordered array of liqu ...

formed in the steam explosions of lava touching down against water, similar to the process that is happening today on Kilauea. This would have built a

black sand beach Black sand is sand that is black in color. One type of black sand is a heavy, glossy, partly magnetic mixture of usually fine sands containing minerals such as magnetite, found as part of a placer deposit. Another type of black sand, found o ...

over time; however, following millions of years of alterations, most of the sand has since been converted into

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay part ...

. Small hills, constructed of jagged lava flows, are thought to have resulted from subaerial

'a'a Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or und ...

flows. The northeast-trending ridges, which are common to the group that Rodriquez Seamount is in, are less distinct on Rodriguez than on the other seamounts in the group. In addition, the seamount is propagated by several large volcanic cones, the largest of which is tall and at the base, with a volume of about . The lower flanks of the volcano have slumped and are covered in a thick layer of sediment, particularly the southwest flank. Another slump area to the west flank has blocky debris on it, suggesting that the base of the volcano has also started collapsing into itself. Rodriguez Seamount once extended above

sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardise ...

, resulting in a flat, sediment-covered summit that is coated with beach sands of ancient origin. This flat top earns it the distinction of being a guyot. These sands have been colonized by, among others,

sea cucumber Sea cucumbers are echinoderms from the class Holothuroidea (). They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of holothu ...

s. An expedition in 2003 included Rodriguez Seamount as one of its destinations. Observations made during the expedition confirmed theories that the seamount had once been above sea level, and has since subsided about from its former height. A sandstone structure discovered at depth seems to hint at a former sand beach and shoreline.

References

{{reflist Seamounts of the Pacific Ocean Guyots