Rodriguez Seamount
Encyclopedia
Rodriguez Seamount is a seamount
and guyot
located about 150 km (93 mi) off the coast of Central California
. It is structurally similar to the nearby Guide
, Pioneer
, Gumdrop
, and Davidson
seamounts, all located roughly between 37.5° and 34.0° degrees of latitude
. 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
which has since been replaced in its role by the San Andreas Fault
system.
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
and Hawaiite
. Ar-Ar dating techniques indicate that the volcano is between 10 and 12 million years of age.
Rodriguez Seamount rises about 1675 m (5,495 ft) above the surrounding seafloor, to a minimum depth of 650 m (2,133 ft). Its calculated volume is greater than 205 km³ (49 cu mi); however this is likely an understatement because the survey did not include its lowermost slope.
The slope is composed mostly of layered volcanic rock
, mostly coarse sandstone
, with a few scattered large lava boulders. They were likely formed from fragments of volcanic glass
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 over time; however, following millions of years of alterations, most of the sand has since been converted into clay
. Small hills, constructed of jagged lava flows, are thought to have resulted from subaerial 'a'a 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 700 m (2,297 ft) tall and 2.2 km (1.4 mi) at the base, with a volume of about 2.6 km³ (0.623773172371145 cu mi). 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
, resulting in a flat, sediment-covered summit that is coated with beach sand
s of ancient origin. This flat top earns it the distinction of being a guyot. These sands have been colonized by, among others, sea cucumber
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 750 m (2,461 ft) from its former height. A sandstone structure discovered at 650 m (2,133 ft) depth seems to hint at a former sand beach and shoreline.
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
and guyot
Guyot
A guyot , also known as a tablemount, is an isolated underwater volcanic mountain , with a flat top over 200 meters below the surface of the sea. The diameters of these flat summits can exceed ....
located about 150 km (93 mi) off the coast of Central California
Central California
Central California, sometimes referenced as Mid-State, is an area of California south of the San Francisco Bay Area and north of Southern California...
. It is structurally similar to the nearby Guide
Guide Seamount
Guide Seamount is a seamount in the eastern Pacific Ocean, about 16.6±0.5 million years old. It is similar in shape and orientation to the nearby Davidson, Pioneer, Rodriguez, and Gumdrop seamounts. It is named for the U.S. National Geodetic Survey survey ship the US&GS Guide.Guide Seamount is...
, Pioneer
Pioneer Seamount
Pioneer Seamount is an undersea mountain, or seamount, in the Pacific Ocean off the coast of central California.-Location:Pioneer Seamount is located at 37° 21.1' North Latitude, 123° 26.1' West Longitude, at the base of the continental slope of North America about 95 kilometers off the coast just...
, Gumdrop
Gumdrop Seamount
Gumdrop Seamount is a small seamount located on the flank of Pioneer Seamount, off the coast of Central California. It is the northern-most of the related seamounts in the region, which includes Davidson, Guide, Pioneer, and Rodriguez seamounts...
, and Davidson
Davidson Seamount
Davidson Seamount is a seamount located off the coast of Central California, southwest of Monterey and west of San Simeon. At long and wide, it is one of the largest known seamounts in the world. From base to crest, the seamount is tall, yet its summit is still below the sea surface...
seamounts, all located roughly between 37.5° and 34.0° degrees of latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
. 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
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
which has since been replaced in its role by the San Andreas Fault
San Andreas Fault
The San Andreas Fault is a continental strike-slip fault that runs a length of roughly through California in the United States. The fault's motion is right-lateral strike-slip...
system.
Geology
Magnetic anomaliesMagnetism
Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Ferromagnetism is the strongest and most familiar type of magnetism. It is responsible for the behavior of permanent magnets, which produce their own persistent magnetic fields, as well...
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
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
and Hawaiite
Hawaiite
Hawaiite is an olivine basalt with intermediate composition between alkali olivine and mugearite. It was first described at the island of Hawaii. In gemology, hawaiite is a colloquial term for Hawaii-originated peridot,which is gem-quality olivine mineral....
. Ar-Ar dating techniques indicate that the volcano is between 10 and 12 million years of age.
Rodriguez Seamount rises about 1675 m (5,495 ft) above the surrounding seafloor, to a minimum depth of 650 m (2,133 ft). Its calculated volume is greater than 205 km³ (49 cu mi); 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
Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it is an igneous rock of volcanic origin...
, mostly coarse sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
, with a few scattered large lava boulders. They were likely formed from fragments of volcanic glass
Volcanic glass
Volcanic glass is the amorphous product of rapidly cooling magma. Like all types of glass, it is a state of matter intermediate between the close-packed, highly ordered array of a crystal and the highly disordered array of gas...
formed in the steam explosions of lava touching down against water, similar to the process that is happening today on Kilauea
Kilauea
Kīlauea is a volcano in the Hawaiian Islands, and one of five shield volcanoes that together form the island of Hawaii. Kīlauea means "spewing" or "much spreading" in the Hawaiian language, referring to its frequent outpouring of lava. The Puu Ōō cone has been continuously erupting in the eastern...
. This would have built a black sand beach over time; however, following millions of years of alterations, most of the sand has since been converted into clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
. Small hills, constructed of jagged lava flows, are thought to have resulted from subaerial 'a'a 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 700 m (2,297 ft) tall and 2.2 km (1.4 mi) at the base, with a volume of about 2.6 km³ (0.623773172371145 cu mi). 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
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
, resulting in a flat, sediment-covered summit that is coated with beach sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
s 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 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. There are a number of holothurian species and genera, many of which are targeted...
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 750 m (2,461 ft) from its former height. A sandstone structure discovered at 650 m (2,133 ft) depth seems to hint at a former sand beach and shoreline.