Proposed: Marine Sanctuary Expansion or Marine National Monument

Part II, The Rodriguez Seamount, part of the Santa Lucia Bank Area Santa Lucia Bank, Santa Lucia Escarpment,
Arguello Canyon and the Persistent Upwelling between Point Conception and Point Sal "Core Area One"

by Carol Georgi and Karl Kempton, former Energy Planner for San Luis Obispo County
and Lead Author of "Proposed Central Coast National Marine Sanctuary, 1990"

Introduction

Special marine places in need of protection can be designated national monuments or be established national marine sanctuaries.

During times of low funding for the national marine sanctuary system, new sanctuaries and extensions can be difficult to achieve. However, designating a special place as a national monument is an alternative that would at least provide national designation and have the potential to upgrade.

For example, Channel Islands began as a national monument, and was later changed to the Channel Islands National Marine Sanctuary.

In 1938 President Franklin D. Roosevelt proclaimed the islands of Anacapa and Santa Barbara as a national monument. Then, in 1980, President Jimmy Carter signed into law a bill abolishing Channel Islands National Monument. He then raised the status of these islands, with the addition of the water surrounding Santa Cruz and Santa Rosa to that of a national park. This area was augmented by the designation of Channel Islands National Marine Sanctuary later that year. The sanctuary boundaries stretch six miles offshore, encircling Santa Barbara Island and the four northern islands. (See: Channel Islands National Park)

The Antiquities Act of 1906 grants the President authority to designate national monuments in order to protect "objects of historic or scientific interest." While most national monuments are established by the President, Congress has also occasionally established national monuments protecting natural or historic features. National monuments are currently managed by agencies including the National Park Service, Forest Service, Fish and Wildlife Service, or Bureau of Land Management (BLM). (See: BLM Heritage Adventures)

For example, the California Coastal National Monument (CCNM) was established by presidential proclamation in 2000. The CCNM is located off the entire 1,100 miles of California coastline in the near shore ocean zone, which begins just off shore and ends at the boundary between the continental shelf and continental slope (about 12 miles). This Monument includes more than 20,000 small islands, rock, exposed reefs, and pinnacles between Mexico and Oregon. The CCNM provides feeding and nesting habitat for an estimated 200,000 breeding seabirds, as well as forage and breeding habitat for marine mammals including the southern sea otters and California Sea lions. The scenic qualities and critical habitat of this public resource are protected as part of the National Landscape Conservation System, administered by the Bureau of Land Management, U.S. Department of the Interior. (See: BLM Special Areas)

National Significance of the Rodriguez Seamount

Our research supports the proposal that the Santa Lucia Bank Area should be designated a marine national monument or an extension to the Channel Islands National Marine Sanctuary. This significant area includes the Santa Lucia Bank, Arguello canyon, and the Rodriguez Seamount. The May article in the SLO Coast Journalfocused on the Santa Lucia Bank and Arguello Canyon. Now we will focus on the Rodriguez Seamount, an underwater mountain.

The Rodriguez Seamount is unique among the California Seamounts in that it was once an island and has a flat top (a guyot) with rugged flanks and extensive flat regions. The Rodriguez Seamount has scientific significance similar to that of the Davidson Seamount to the north. The Monterey Bay National Marine Sanctuary added the Davidson Seamount by extension in 2009 becauseit has special national significance to ocean conservation, ecological, scientific, educational, aesthetic, and historical qualities. (See:Monterey Bay)

Our research found the Rodriguez Seamount to be as nationally significant as the Davidson Seamount, and therefore needs to also be protected by either a national marine sanctuary extension or by national monument designation. The Monterey Bay Aquarium Research Institute (MBARI) is an excellent source for information about the Rodriguez Seamount, which is located offshore Santa Barbara in the Santa Lucia Bank area near the Channel Islands National Marine Sanctuary. Below are three images of the Rodriguez Seamount from MBARI.

Detailed Images of Rodriguez Seamount Summit

Rodriguez is called a guyot because it has a distinctive flat top with a sharp break-in-slope at 700 m depth, suggesting wave planation at sea level after volcanic activity ceased.

Perspective View From the South Click on images for larger versions.

MBARI identifies the Rodriguez Seamount as a Guyot (a flat-topped submarine mountain), located about halfway up the continental rise, offshore Santa Barbara. It is structurally similar to the Davidson Seamount, located farther north at the base of the continental slope about 150 km off the central California coast. The Rodriguez Guyot rises about 1,675 meters above the surrounding seafloor to a minimum water depth of 650 meters.

The MARI posts many of the logs of their expeditions studying the Rodriguez Seamount. Below is an excerpt of one such expedition by David Clague. (See also: MBARI Expeditions)

Monterey Bay Aquarium Research Institute Log Book
Seamounts 2003
October 11- October 17, 2003

A map showing the location of Rodriguez Seamount, off Point Conception. Click on map to enlarge.

October 13, 2003
David Clague writes:

The observations we made today confirm the hypothesis that Rodriguez Seamount was an island at one time and that it has subsided about 700-750 m since it formed. Rodriquez was surrounded by sand beaches and cobble beaches formed where lava flowed into the sea. Inland areas included a few thick lava flows erupted from vents located near the center of the summit platform. The subsidence of the island below sea level most likely occurred
when the seamount approached the subduction zone that lay offshore California before the San Andreas Fault formed.

Marine Life on the Rodriguez Seamount

The Rodriguez Seamount, a volcanic geological formation, is about 90 miles offshore in the southern area of the opening of the Arguello Canyon. Whether the submerging of the seamount was caused by internal volcanic collapse, a victim of tectonic forces or a combination of both is a research project. Its topography is complex with many volcanic cones, one of which is among the largest found along the California coast. Being located on the Arguello Canyon's south face with the San Miguel Gap to its south, and located in a meeting place of cold and warm currents, the Rodriguez Seamount hosts a complex marine habitat. The sandy beach remnants, for example, have been colonized by a large number of sea cucumbers. Other seamounts have few if any sea cucumbers. There has yet to be a comparison of marine life between the walls of the Arguello Canyon and the Rodriguez Seamount.

What has been found is significant. "Amazingly, biological communities varied significantly even in similar habitats at similar water depths on different parts of Rodriguez Seamount. The seamount's megafauna consist of a vast array of sponges, including large, brilliant-yellow barrel sponges, many types of coral—including large gorgonians and huge golden coral seafans—abundant brittlestars, crinoids, clams, seastars, polychaete worms, crabs, tunicates, sea urchins, sea cucumbers, octopi, and many more. The giant sponges housed communities of other organisms. New species were found, and some species were rediscovered after not being observed for decades."

Geologists and Biologists Endeavor to Understand Seamount Environments Off California, Jim Hein Dec. 2003 / Jan. 2004

Oceanographic Setting: Channel Islands and Rodriguez Seamount

The geologic features—the Channel Islands and the former island, the Rodriguez Seamount—are part of the Arguello Microplate to our south. As shown in last month's article, these were once part of the mainland coastline previously aligned in the typical west coast North-South direction. Last month's article contained maps and animation illustrating the movement of the microplate section, now holding the islands offshore, in a clockwise rotation caused by tectonic forces of three tectonic plates, the North American, Farallon and Pacific. The maps below illustrate these forces on the Channel Islands and its surrounding complex submerged marine habitat.

At the meeting place of the two local microplates, the south face of the Arguello Canyon and the Rodriguez Seamount are on the Arguello Microplate. The north face of the canyon is on the Monterey Microplate. The twisting and realignment of the Southern California coastline from this microplate meeting place and the formation of the Arguello Canyon has played a significant role in creating a boundary of two Oceanographic and Meteorological Provinces in this area. But, the exact forces and narrative remain to be researched and finalized because the offshore and nearshore areas west of the San Andreas are still in the process of being studied. While the land side of the San Andreas is among the most studied fault zones in the world, the nearshore and offshore zone is considerably under studied given the potential threats to a coastal located nuclear power plant.

What is known is that on top of the  Arguello Microplate,  the Western Transverse block was rotating against the North American Plate at the the San Andreas Fault’s large curve, the Big Bend. It rotated over a few million years between 80 to 110 degrees swinging the Channel Islands off what is now Santa Barbara. The rotation ceased when the two microplates upon which Baja sits, the Magdalena and Guadalupe Microplates, were captured by the Pacific Plate and jammed it against the Arguello Microplate. Since that time, uplift has been taking place. The Arguello Microplate is being squeezed in a North-South direction because it is pinned against the Big Bend as the Magdalena and Guadalupe Microplates to the south continue to rift causing an expansion. For details see Past is Key: Tectonic Evolution of the Pacific-North American Plate Boundary and Its Implications for Crust/Mantle Structure and Current Plate Boundary Strain (pdf file)

Note that the Transverse Mountain Range complex runs East-West. It was once aligned North-South. All other California mountain ranges are aligned North-South. As a result of these forces, several uptrust faults have formed. Remember the Northridge quake of 1989? The Santa Monica Mountains grew eight inches in seconds. For those of us living a few miles to the North of this tectonic force pressed microplate, we should demand considerable research to determine what pressures are being applied to our microplate and what if any uptrust faults are hidden along these microplate boundaries.

For more overviews, see Neogene Deformation History of Western North America and Volcanism in Coastal California

In conclusion, we provide several maps with descriptions of tectonic history, plate movement and major fault activity of the oceanographic setting of the Channel Islands and the Rodriguez Seamount. The last map, the "Simplified Fault Activity Map of California," shows 5 thrust faults offshore, all within about 50 miles of Diablo Canyon Nuclear Power Plant. Notice especially, the two upthrust faults between the Hosgri and the Santa Lucia faults, and the upthrust fault just south of the Hosgri fault.

Figure 2.2. Tectonic History of the Transverse Ranges (TR), Outer Borderlands (OB), and Inner Borderlands (IB) showing left to right (1) the initial collision of the Pacific and North America plates, (2) transtension and the rotation of the Transverse Ranges Block and (3) transpression, the current San Andreas dextral transform fault system, and the extrusion of the Transverse Ranges block around the larger transpressional bend of the San Andreas (after Atwater, 1998)

Geology and Geomorphology of Eastern Santa Cruz Island Field Guide; Chapter 2, page 9

Figure 4.1. [A] Location map of Southern California with major faults, tectonic provinces, and relative motion of the Pacific Plate with respect to a stable North America. [B] Fault map of the western Transverse Ranges and Northern Channel Islands. Maps and geology simplified from Atwater (1998) and Chaytor et al. (2008).

Geology and Geomorphology of Eastern Santa Cruz Island Field Guide; Chapter 4, page 31

Figure 4.3. Schematic fault and deformation map of the Western Transverse Ranges. White arrows indicate relative motions on opposite sides of major faults; green ellipse is the approximate extent of the Western Transverse Ranges; red arrows show approximate north-south compression and westward directed extension of the TR; orange and white strain ellipses show the pre- and syn-deformation kinematics of the Western TR (respectively) with the eastern end "pinned" against the Big Bend of the SAF. Abbreviations: SAF- San Andreas Fault; BB- Big Bend of the SAF; GF- Garlock Fault; SBMB- San Bernadino Mountains Bend; ST- Salton Trough; SJF- San Jacinto Fault; EF- Elsinore Fault.

Geology and Geomorphology of Eastern Santa Cruz Island Field Guide; Chapter 4, page 33

Selected section for our area from
SIMPLIFIED FAULT ACTIVITY MAP OF CALIFORNIA
Compiled by Charles W. Jennings and George J. Saucedo
1999 (Revised 2002, Tousson Toppozada and David Branum) PDF]

SIMPLIFIED FAULT ACTIVITY MAP OF CALIFORNIA
File Format: PDF/Adobe Acrobat - Quick View

Banner Image of Otter & Pup by Cleve Nash