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Seafloor geology plays a major role in habitat formation and can be used to remotely identify key habitats for some commercially important fish species. We have used a combination of side-scan sonar mosaics, multibeam bathymetry, and backscatter data, and in situ observations and video from the submersible Delta to investigate marine benthic habitats in the Eastern Gulf of Alaska. The intent of this paper is to review the results of previous marine benthic habitat mapping efforts completed by us along the transform plate boundary of Alaska and to present new information that show how volcanic, plutonic, and glacial submarine geomorphology can be used to identify potentially important discrete habitat areas. Demersal shelf rockfish, a seven-species management complex of nearshore rockfish, including yelloweye rockfish ( Sebastes ruberrimus ), are found in rugged and highly rugose geomorphologic features. Eroded volcanic edifices, lava fields, and a pit crater, as well as a small shutterridge, deformed and differentially eroded sedimentary bedrock, and highly fractured and faulted plutonic rock outcrops are features that attract adult rockfish. Volcanic edifices that lie along the leaky (magma-conducting) Fairweather transform fault system intercept ocean currents, in turn producing upward eddies that bring nutrients to species residing on the features. We show that geologic processes such as fault deformation, volcanism, and glaciation are critical to the development of Essential Fish Habitats (EFH) for demersal shelf rockfish. Our work is the first attempt to determine a common geologic link between desperate commercial fishing areas in SE Alaska, USA, and to suggest how tectonic and glacial processes, including sea level rise and transgression, can be used to identify seafloor geologic characteristics as surrogates for marine groundfish habitats.

A large submarine landslide complex and four small landslides developed under the Santa Barbara Channel, suggesting a potential hazard from landslide-generated tsunamis. We integrate offshore stratigraphy and geologic structure, multibeam bathymetric information, and several kinds of seismic-reflection data to understand how and when the submarine landslides formed. Seismic-reflection data show that mass failure along the slope began at least 200 ka ago. Landslides appear as zones of poor reflectivity having an irregular upper surface, and these zones alternate vertically with strong parallel reflections. The emplacement ages of two of the three main landslide lobes are well established at 8 and 10 ka. The source material for the youngest part of the landslide complex was sediment of probable late Pleistocene and Holocene age that accumulated in a shelf-edge delta. Directly under this delta, growth of faults and anticlines was particularly intense and tended to oversteepen the deltaic deposits. These active structures also formed migration pathways and reservoirs for aqueous and hydrocarbon fluids from the deep basin. Tsunami deposits have been described from a low-lying area near Santa Barbara, and numerical modeling of tsunamis generated by hypothetical landslides in Santa Barbara Channel indicates a moderate to severe threat [Borrero, J.C., Dolan, J.F. and Synolakis, C.E., 2001. Tsunamis within the eastern Santa Barbara Channel. Geophys. Res. Lett., 28(4): 643–646.], involving wave runups of 2–20 m, for a range of assumed landslide volumes. Inundation from these waves, however, is expected to be highly focused so that only narrow (∼10-km) sections of the shoreline would be affected.

High-resolution swath bathymetry and backscatter data from the Santa Barbara basin reveal a distinct assemblage of morphologic and sedimentologic features characteristic of the tectonically active setting of the basin. Such characteristics include the north–south asymmetry of the basin, the presence of an intra-basinal structural and morphologic high, extensive mass wasting, and fields of mounds and pockmarks. The north–south asymmetry of the basin and the increased abundance of slope failure along the northern basin slope likely reflect higher rates of tectonic shortening and sediment accumulation along the northern basin margin. High sedimentation rates lead to high pore water content of the sediment which, in combination with seismic shaking, may explain the abundance of mass wasting features even on shallowly inclined lower basin slopes. Mounds and pockmarks are the surface expression of locally extensive fluid seepage which we interpret to be driven by a combination of high sedimentation rates, a high organic content of sediment, and anoxic bottom water conditions during extended periods in Neogene and Quaternary times. During ROV dives we observed active fluid seepage to have occurred preferentially on the shelf and on a structural and topographic high, presumably due to structural focusing of migrating formation fluids. The preferred alignment of some pockmarks along faults is consistent with structurally controlled expulsion of formation fluids from underlying Neogene units. Despite the high tectonic activity of the basin, fault scarps are rare and only observed in areas of low sediment accumulation on the shelf and on topographic highs. Mass balance considerations suggest that sedimentation rates averaged over interseismic time scales are too high and scarp growth rates too low for scarps to be characteristic features of the basin floor. Long-term sediment accumulation rates that account for the effect of sediment compaction are low enough, however, to lead to long-wavelength surface expressions of the most active faults.

This part of SIM 3302 presents data for part of the acoustic-backscatter map (see sheet 3, SIM 3302) of the Offshore of Coal Oil Point map area, California. The raster data file is included in "BackscatterC_Fugro_OffshoreCoalOilPoint.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreCoalOilPoint/data_catalog_OffshoreCoalOilPoint.html. The acoustic-backscatter map of the Offshore of Coal Oil Point map area, California, was generated from backscatter data collected by California State University, Monterey Bay, Seafloor Mapping Lab (CSUMB), by the U.S. Geological Survey (USGS), and by Fugro Pelagos. These metadata describe the acoustic-backscatter data collected by Fugro Pelagos and reprocessed by CSUMB. See "BackscatterA_CSUMB_OffshoreCoalOilPoint_metadata.txt" metadata for a description of the acoustic-backscatter data collected by CSUMB, and see "BackscatterB_USGS_OffshoreCoalOilPoint_metadata.txt" metadata for a description of the acoustic-backscatter data collected by the USGS. Fugro Pelagos collected backscatter data offshore the Coal Oil Point region (part of a larger Southern California mapping effort) using a combination of several sonars (400-kHz Reson 7125, 240-kHz Reson 8101, 100-kHz Reson 8111) aboard a series of Fugro Pelagos-directed vessels. An Applanix POS MV (Position and Orientation System for Marine Vessels) was used to accurately position the vessels during data collection, and it also accounted for vessel motion such as heave, pitch, and roll (position accuracy, +/-2 m; pitch, roll, and heading accuracy, +/-0.02 degrees; heave accuracy, +/-5 percent, or 5 cm). KGPS (GPS with real-time kinematic corrections) altitude data were used to account for tide-cycle fluctuations, and sound-velocity profiles were collected with an Applied Microsystems SVPlus sound velocimeter. Data were cleaned, and final products were created by the Seafloor Mapping Lab at CSUMB from the postprocessed multibeam-bathymetry data. Within the acoustic-backscatter imagery, brighter tones indicate higher backscatter intensity, and darker tones indicate lower backscatter intensity. The intensity represents a complex interaction between the acoustic pulse and the seafloor, as well as characteristics within the shallow subsurface, providing a general indication of seafloor texture and sediment type. Backscatter intensity depends on the acoustic source level; the frequency used to image the seafloor; the grazing angle; the composition and character of the seafloor, including grain size, water content, bulk density, and seafloor roughness; and some biological cover. Harder and rougher bottom types such as rocky outcrops or coarse sediment typically return stronger intensities (high backscatter, lighter tones), whereas softer bottom types such as fine sediment return weaker intensities (low backscatter, darker tones).

Remotely operated vehicle (ROV)-based mapping of tectonic features, zones of anomalous reflectivity, and geomorphic targets in Monterey Bay, California, demonstrates the regional abundance of fluid expulsion along the active transform margin between the Pacific and North American plates. Cold seeps—extant communities characterized by chemosynthetic bivalves, bacterial mats, and rare tubeworms—are the surface manifestations of present-day fluid expulsion of sulfide- and methane-rich fluids, whereas slabs, veins, and chimneys of authigenic carbonate represent regions of either dormant methane-rich fluid expulsion, or areas where the present rate of flow is too low to support chemosynthetic fauna. We have found both active and dormant fluid seepage along fault zones, at the surface expression of mud volcanoes, on organic-rich or permeable substrate, and within headless canyons across a wide range of depths within Monterey Bay. The fluid egress at these sites may be driven by a combination of (1) pore-space reduction caused by rapid sedimentation and/or tectonic compaction related to residual Pacific–North America compression, and (2) increased buoyancy due to a decrease in pore-fluid density related to diagenesis and/or catagenesis at depth. Although provocative, the relationship between topographically driven aquifer discharge and sea-floor fluid expulsion remains speculative for Monterey Bay. The widespread distribution of fluid expulsion features controlled by a variety of conduits in Monterey Bay implies that cold seeps may be common features on translational margins.

The Ascension-Monterey Canyon system, one of the largest submarine canyon systems in the world, is located offshore central California. The system is composed of two parts which contain a total of six canyons: 1) the Ascension part to the north, which includes Ascension, Ano Nuevo and Cabrillo Canyons, and 2) the Monterey part to the south, which includes Monterey Canyon and its distributaries, Soquel and Carmel Canyons. These six canyons have a combined total of 16 heads: one head each for Ascension, Soquel and Monterey Canyons, two heads for Ano Nuevo Canyon, three heads for Carmel Canyon, and eight heads for Cabrillo Canyon. Ascension, Ano Nuevo and Cabrillo Canyons coalesce in 2,300 m of water to form the Ascension Fan-Valley. Soquel and Carmel Canyons join Monterey Canyon at depths of 915 m and 1,900 m, respectively, to form Monterey Fan-Valley (the main channel of the system). Ascension Fan-Valley joins Monterey Fan-Valley on the proximal part of Monterey Fan in 3,290 m of water. The Ascension-Monterey Canyon system has a long and varied history. The ancestral Monterey Canyon originated in early Miocene time, cutting east-west into the crystalline basement of the Salinian block (possibly subaerially), somewhere near the present location of the Transverse Range of California. Since that time (∼21 Ma), the Salinian block, riding on the Pacific Plate, moved northward along the San Andreas fault zone. During this period of transport the Monterey Bay region was subjected to several episodes of submergence (sedimentation) and emergence (erosion) that alternately caused sedimentary infilling and exhumation of Monterey Canyon. The present configuration of the Ascension-Monterey Canyon System is the result of tectonic displacement of a long-lived submarine canyon (Monterey Canyon), with associated canyons representing the faulted offsets of past Monterey Canyon channels. Slivering of the Salinian block along several fault zones trending parallel or sub-parallel to the San Andreas fault zone (the Ascension fault and the Palo Colorado-San Gregorio fault zone, in particular) displaced to the north the westerly parts of Monterey Canyon. In this manner Monterey Canyon “fathered” Cabrillo Canyon, Ano Nuevo Canyon, Ascension Canyon and Pioneer Canyon, along with an unnamed canyon located between Ascension and Pioneer Canyons. Tectonics continue to dictate the morphology and processes active in the system today. The Palo Colorado-San Gregorio fault zone marks the continental shelf boundary in the Monterey Bay region and divides the canyon system into two parts, the Ascension and Monterey parts. The Monterey Canyon part has a youthful, V-shaped profile while the Ascension part, except for the heads that notch the shelf, and both fan-valleys exhibit more mature, U-shaped profiles. Earthquakes stimulate mass-wasting on the continental slope; most of the Ascension part of the system now receives its sediment from this source. The Monterey part, however, intercepts sediments carried by longshore transport and is the main regional conduit for terrestrial sediment transport to the abyssal plain.

Detailed sampling of the axis and flanks of upper Monterey Canyon (water depths of

As a result of the October 17, 1989, Loma Prieta (Santa Cruz Mountains, California) earthquake, liquefaction of the fluvial, estuarine, eolian, and beach sediments under a sand spit destroyed the Moss Landing Marine Laboratories and damaged other structures and utilities. Initial studies suggested that the liquefaction was a local phenomenon. More detailed offshore investigations, however, indicate that it occurred over a large area (maximum 8 km{sup 2}) during or shortly after the earthquake with movement of unconsolidated sediment toward and into the head of Monterey submarine canyon. This conclusion is supported by side-scan sonographs, high-resolution seismic-reflection and bathymetric profiles, onshore and sea-floor photographs, and underwater video tapes. Many distinct lobate features were identified on the shallow shelf. These features almost certainly were the result of the October 17 earthquake; they were subsequently destroyed by winter storms. In addition, fresh slump scars and recently dislodged mud debris were found on the upper, southern wall of Monterey submarine canyon.

Seismic reflection profiles and magnetic intensity measurements were collected across the southern continental margin of Spain and the Alboran basin between Spain and Africa. Correlation of the distinct seismic stratigraphy observed in the profiles to stratigraphic information obtained from cores at Deep Sea Drilling Project site 121 allows effective dating of tectonic events. The Alboran Sea basin occupies a zone of motion between the African and Iberian lithospheric plates that probably began to form by extension in late Miocene time (Tortonian). At the end of Miocene time (end of Messinian) profiles show that an angular unconformity was cut, and then the strata were block faulted before subsequent deposition. The erosion of the unconformity probably resulted from lowering of Mediterranean sea level by evaporation when the previous channel between the Mediterranean and Atlantic was closed. Continued extension probably caused the block faulting and, eventually the opening of the present channel to the Atlantic through the Strait of Gibraltar and the reflooding of the Mediterranean. Minor tectonic movements at the end of Calabrian time (early Pleistocene) apparently resulted in minor faulting, extensive transgression in southeastern Spain, and major changes in the sedimentary environment of the Alboran basin. Active faulting observed at five locations on seismic profiles seems to form a NNE zone of transcurrent movement across the Alboran Sea. This inferred fault trend is coincident with some bathymetric, magnetic and seismicity trends and colinear with active faults that have been mapped on-shore in Morocco and Spain. The faults were probably caused by stresses related to plate movements, and their direction was modified by inherited fractures in the lithosphere that floors the Alboran Sea.

Ascension Submarine Canyon, which lies along the strike-slip (transform) dominated continental margin of central California, consists of two discrete northwestern heads and six less well defined southeastern heads. These eight heads coalesce to form a single submarine canyon near the 2700 m isobath. Detailed seismic stratigraphic data correlated with 19 rock dredge hauls from the walls of the canyon system, suggest that at least one of the two northwestern heads was initially eroded during a Pliocene lowstand of sea level ∼3.8 m.y. B.P. Paleogeographic reconstructions indicate that at this time, northwestern Ascension Canyon formed the distal channel of nearby Monterey Canyon and has subsequently been offset by right-lateral, strike-slip faulting along the San Gregorio fault zone. Some of the six southwestern heads of Ascension Canyon may also have been initially eroded as the distal portions of Monterey Canyon during late Pliocene-early Pleistocene sea-level lowstands (∼2.8 and 1.75 m.y. B.P.) and subsequently truncated and offset to the northwest. There have also been a minimum of two canyon-cutting episodes within the past 750,000 years, after the entire Ascension Canyon system migrated to the northwest past Monterey Canyon. We attribute these late Pleistocene erosional events to relative lowstands of sea level 750,000 and 18,000 yrs B.P. The late Pleistocene and Holocene evolution of the six southeastern heads also appears to have been controlled by structural uplift of the Ascension-Monterey basement high at the southeastern terminus of the Outer Santa Cruz Basin. We believe that uplift of this basement high sufficiently oversteepened submarine slopes to induce gravitational instability and generate mass movements that resulted in the erosion of the canyon heads. Most significantly, though, our results and interpretations support previous proposals that submarine canyons along strike-slip continental margins can originate by tectonic trunction and lateral offset.