Farallon plate was subducted under the west coast of the American continent
(Lipman et al. 1971), the EPR segments continued off the coast of California and
Oregon and joined with the Juan de Fuca and other northern spreading ridge
segments. The San Andreas Fault, which is subaerial, roughly follows the trace of
the subduction zone at the west of the northern part of California before it joins the
undersea Mendocino fracture zone and the Gorda Ridge spreading segment near
40°20
0 N.
The consequences of the Pacific plate plunging underneath the North American
continent gave rise to the Cascade Mountains and contributed to the volcanism of
the Cascade Range provinces (DeMets et al. 1990; Flueh et al. 1998) in Arizona,
California, Utah, Oregon and up to the State of Washington. As a result of the
Pacific plate’s plunge, there has been recent Quaternary volcanism in the Cascades
Range such as that observed at Mt. St. Helens, Mt. Rainier in Washington
(Olympic Mountain area), Crater Lake in Oregon, and Lassen Peak in California.
The EPR consists of ridge segments that have the most variable spreading rates
when compared to those from other Indian and Atlantic accreting ridge systems.
The spreading rates vary between 5 cm/yr to 18 cm/yr (total rate) all along its
length. The variable spreading rate reflects the speed and volume of magma
delivery, which also influences the ridge segments’ axial morphology and volcanic
activity. On the basis of bathymetric results obtained between 21°N (Gulf of
California) down to the colder ocean near the coast of Antarctica around 50°S, it is
now well established that the accreting plate boundary of the EPR is neither a
linear nor a continuous feature. On the contrary, the EPR is formed by short
volcanic segments varying in length between a few kilometers (\10 km) up to
more than hundreds of kilometers (100–500 km).
East Pacific Rise at 21°N
After the success of project FAMOUS with its international group of scientists and
personnel using surface ships and submersibles for a detailed investigation in the
North Atlantic, the French and Americans decided to continue a similar collaboration in order to study fast-spreading ridge segments. The idea for this new
project was first discussed among the scientists involved on project FAMOUS,
while they were on board the Marcel Le BIHAN in 1974.
From 1975–1977, scientists from CNEXO-IFREMER, Scripps Institution in
San Diego (California), the U.S. Geological Survey, and WHOI (Woods Hole
Oceanographic Institution) were involved in a project called ‘‘RITA’’ (acronym
given for two transform faults named the Rivera and Tamayo after two Mexican
painters) (Fig. 7.13). The leaders of the project were both experts in geophysical
prospecting : Jean Francheteau (for the French group, from CNEXO) and Fred
Spiess (for the American group, from the Scripps Institution, University of California in San Diego). Previous work of mapping and deep-towed geophysical
investigations in the area had been mostly done by U.S. institutions and had
The East Pacific Rise
199
(Lipman et al. 1971), the EPR segments continued off the coast of California and
Oregon and joined with the Juan de Fuca and other northern spreading ridge
segments. The San Andreas Fault, which is subaerial, roughly follows the trace of
the subduction zone at the west of the northern part of California before it joins the
undersea Mendocino fracture zone and the Gorda Ridge spreading segment near
40°20
0 N.
The consequences of the Pacific plate plunging underneath the North American
continent gave rise to the Cascade Mountains and contributed to the volcanism of
the Cascade Range provinces (DeMets et al. 1990; Flueh et al. 1998) in Arizona,
California, Utah, Oregon and up to the State of Washington. As a result of the
Pacific plate’s plunge, there has been recent Quaternary volcanism in the Cascades
Range such as that observed at Mt. St. Helens, Mt. Rainier in Washington
(Olympic Mountain area), Crater Lake in Oregon, and Lassen Peak in California.
The EPR consists of ridge segments that have the most variable spreading rates
when compared to those from other Indian and Atlantic accreting ridge systems.
The spreading rates vary between 5 cm/yr to 18 cm/yr (total rate) all along its
length. The variable spreading rate reflects the speed and volume of magma
delivery, which also influences the ridge segments’ axial morphology and volcanic
activity. On the basis of bathymetric results obtained between 21°N (Gulf of
California) down to the colder ocean near the coast of Antarctica around 50°S, it is
now well established that the accreting plate boundary of the EPR is neither a
linear nor a continuous feature. On the contrary, the EPR is formed by short
volcanic segments varying in length between a few kilometers (\10 km) up to
more than hundreds of kilometers (100–500 km).
East Pacific Rise at 21°N
After the success of project FAMOUS with its international group of scientists and
personnel using surface ships and submersibles for a detailed investigation in the
North Atlantic, the French and Americans decided to continue a similar collaboration in order to study fast-spreading ridge segments. The idea for this new
project was first discussed among the scientists involved on project FAMOUS,
while they were on board the Marcel Le BIHAN in 1974.
From 1975–1977, scientists from CNEXO-IFREMER, Scripps Institution in
San Diego (California), the U.S. Geological Survey, and WHOI (Woods Hole
Oceanographic Institution) were involved in a project called ‘‘RITA’’ (acronym
given for two transform faults named the Rivera and Tamayo after two Mexican
painters) (Fig. 7.13). The leaders of the project were both experts in geophysical
prospecting : Jean Francheteau (for the French group, from CNEXO) and Fred
Spiess (for the American group, from the Scripps Institution, University of California in San Diego). Previous work of mapping and deep-towed geophysical
investigations in the area had been mostly done by U.S. institutions and had
The East Pacific Rise
199