UC San Diego Bibliography Title La Jolla Canyon and Scripps Canyon Bibliography Permalink https://escholarship.org/uc/item/5079n1d7 Author Brueggeman, Peter Publication Date 2009-10-15 eScholarship.org Powered by the California Digital Library University of California La Jolla Canyon and Scripps Canyon Bibliography Peter Brueggeman Scripps Institution of Oceanography Library Francis Shepard’s classic map of the La Jolla Canyon (left) and Scripps Canyon (right), superceded by modern charting This bibliography is intended to be comprehensive for published research on the Canyons, including selected non-scientific publications. Annotations are included for many publications so that the reader can learn a lot about the Canyons without chasing down individual publications. The bibliography is arranged from the most recent to the oldest. To assist in reading this bibliography, some background information on the canyons is first provided. Most of the publications cited in this bibliography are available in the collection of the Scripps Institution of Oceanography Library, which is open to the public. Scripps Canyon (above right) is a narrow gorge about one mile long with three main branches: North, Sumner and South Branches. All three heads can be traced into the coastal cliffs as incised land canyons. Scripps Canyon is cut into calcareous and noncalcareous mudstone and sandstone of the Eocene Ardath Shale (formerly Rose Canyon Shale), including a large amount of conglomerate, as seen in the sea cliffs to the north. Scripps Canyon has precipitous, narrow, sometimes overhanging rocky walls nearly its entire length, with some sections so narrow that submersibles cannot descend to the bottom. Canyon walls can have scoured and grooved surfaces under the overhanging walls, showing that active erosion is taking place. A well-recognized feature of Scripps Canyon is the cable stretching across the narrow South Branch of Scripps Canyon. James Stewart, retired Diving Officer of Scripps Institution of Oceanography, said the cable was called Beal's Cable when he arrived at Scripps in 1951, so the cable pre-dates 1951. Alan Beal worked for/with Francis Shepard, a Scripps geology professor. Shepard conducted and published research in La Jolla and Scripps canyons, where much of the early research on formation and geological processes in underwater canyons was done. Beal's Cable was laid by E.R. (Ellis Royal) Cross of the Sparling School of Diving and Underwater Welding in Wilmington, California, who was hired to lay it. Francis Shepard of Scripps would be the obvious candidate for the scientist who arranged for ER Cross to lay that cable. Douglas Inman and Jim Stewart, both said that Beal's Cable had conduit in it and was laid from the old Scripps Pier to a future underwater site to be north of Scripps Canyon to enable connection with measuring instruments on the Scripps Pier. The cable-laying ship's captain became concerned about being too close to shore and mis-laid it across the canyon where it is today, and was not used. When the sand cleared out underwater in 1955 or 1956 exposing the hard bottom, Jim Stewart followed the cable laying along the hard bottom all the way back underwater to just about to the old pier (which was located adjacent to the current Scripps Pier on its north side; the old pier was shorter than the current pier too). Jim agrees with George Spalding's observation on the northern termination of Beal's Cable. George said "...I believe that the cable that transits the South branch terminates at about 80 feet at the junction of the main channel of the Sumner branch and the channel marked on the newer map as the Intermediate Branch. This is the branch that turns south. There is about three feet of cable protruding from the wall there, sticking out of the sand in about the right spot. ..." La Jolla Canyon (above left) is wider than Scripps Canyon and has at its head a series of gullies cut into semi-consolidated Pleistocene mud with invertebrates boring and burrowing in the mud. Lower down, La Jolla Canyon cuts through Eocene and Cretaceous rocks. La Jolla Canyon has a wide bowl near the head, but a much narrower rock gorge with steep walls is entered at 400 feet. A littoral cell is a stretch of coastline containing a complete sedimentation cycle that cycles sand on and off the beaches. Bounded by the beach on one side and extending seaward to just beyond the area of breaking waves, a littoral cell is the region where wave energy dissipates. Sediments from rivers and from coastal erosion as well as plant detritus and garbage are moved southward along the coastline from Dana Point to La Jolla within the Oceanside Littoral Cell, until these materials encounter the heads of the Scripps and La Jolla Submarine Canyons. These sediments are transported down the canyons, sometimes as rapidly-moving turbidity current flows which further erode the canyon floors and walls. Both canyons have extensive detrital mats, particularly in their shallower reaches, consisting of surfgrass and kelp detritus and supporting a natural macrofaunal community whose combined density is an order of magnitude larger than that reported anywhere else in the world. Scripps Canyon joins La Jolla Canyon at a depth of about 900 feet, and the two continue seaward as a rock-walled canyon to about 1,600 feet, where a fan valley cut into unconsolidated sediment is encountered. Both canyons have a series of steps along their axes, some with rock lips with a vertical drop of ten feet or more, whereas others have steep sediment-covered slopes a few feet high, suggestive of landslide scars. The submarine fan emptying from La Jolla Canyon into the San Diego Trough is creased by a steep-sided valley that hooks south. Complex natural levees are present continuously along the right bank of the valley but poorly developed along the left except for the outer third. Terraces are well developed in the central portion adjacent to the inner channel, are intermittent and at variable heights in the middle portion, and are inconspicuous along the outer valley. The valley lacks distinct distributaries, although remnants may exist along the outer part. There are precipitous walls along the outside of the bends of the winding channel. Slumping is taking place actively from these walls and large slump blocks of clay are common on the floor. How does the sediment mixed with detritus on the canyon bottoms flush out occasionally? Dr. JH van den Berg of the Department of Physical Geography at Utrecht University offers this explanation: Breaching is defined as the gradual retrogression of a very steep subaqueous slope, steeper than the angle of repose in clean, fine sand. Before particles on a steep slope can be entrained by gravity, their packing has to be changed from a dense to a loose state. As a result negative pore pressures are created in the bed which increase shear resistance and therefore retard erosion. This effect is only important in case the negative pressure is released slowly, thus at relatively low permeability in fine sands combined with a high erosion rate. In the case of gravity, due to shear dilatancy and resulting negative pore pressure, steep slopes up to vertical can exist for some time in fine sands. These breaches retrograde at a velocity in the order of mm/s, dictated by permeability. Two types of breaches are distinguished, (I) with or (II) without a hydraulic jump. Type II breaches retrograde in steep bar slopes. In nature the steep slope may be left behind by the scar of a slide. This type of breach produces a quasi-steady turbidity current. Sustained low energy conditions indicated by thick, massive sand layers preserved in ancient tidal sediments suggest deposition by such a breach generated flow. In contrast to a liquefaction flow slide, a breach retrogrades slowly and may be active for a number of hours. Modern channel bank failures of sands may last for hours, suggesting that breaching is a rather common type of failure in some environments. The periodic 'flushing' of sands from the heads of submarine canyons may also be related to the breaching process. The origin of sustained quasi-steady high-density turbidity currents suggested by the occurrence of massive sandstones in ancient deep-water turbidite successions can be explained in this way. Such canyon breaching fits well with the observation that not all canyon tributaries flush when a storm hits, and that periods of strong waves only occasionally seem to be followed by a flushing event. Since breaching follows from local slope oversteepening, it can explain the erratic nature of these events in time and space [van den Berg, JH, 2001 personal communication, & Sedimentology 49(1):81-95, 2002]. Extraordinarily high secondary productivity is fueled by the kelp and surfgrass detritus at the head of the La Jolla and Scripps Canyons. What's secondary production? The energy-rich organic material (biomass) created through photosynthesis and embodied within the photosynthetic organisms is consumed and converted into other forms. The biomass of these organisms eating the photosynthetic organisms constitute secondary production. A study examined the surfgrass and kelp detrital mat on the floor of La Jolla and Scripps Canyons. Crustaceans inhabited this mat, achieving densities of more than three million individuals and biomass exceeding one kilogram (dry weight) per square meter at times. The combined maximum density of these animals was 3,240,000 individuals per square meter, an order of magnitude greater than any natural macrofaunal assemblage reported in the literature. Fish prey on these detrital mat crustaceans and are thus the tertiary predators in this ecosystem. Localized productivity hotspots in underwater canyons may be an important energy supply for fish production along some coasts [Vetter, EW.