HR: 1340h
AN: H53C-1406    [Abstracts]
TI: Geomorphic Processes Along the Coastal Cliff, Central Coastline – Israel
AU: * Schwartz, J Y
EM: jonathanschwartz@fs.fed.us
AF: National Forest Service, 30800 Bouquet Cyn Rd., Saugus, CA 91390,
AB: A study aimed at finding the nature, rate and causes of the morphological changes in the coastal cliff in central part of Israeli coastline, was carried out between 1991 and 1996, along the coast of Michmoret – Giv'at Olga, Israel. The stratigraphical sequence of this cliff, which is of Pleistocene age, consists of alternating layers of Kurkar (a carbonate cemented quartz eolianite) and Hamra (a red brown sandy loam). The morphological changes occurring in the coastal cliff were documented, prior, during and immediately after storms, by field observation, redundant surveying and photography. The retreat of the coastal cliff is composed of several steps. As a rule the moisture level in the Hamra layers is higher than that of the Kurkar layers because of the higher content of silt and clay in the Hamra. During the rainy season the increase of moisture in the Hamra increases the relative weight and lowers its friction. This in turn intensifies the process of rill development in the Hamra layers and slides of material from this layer occur. As a result the overlying Kurkar remains without support, until the overhanging Kurkar breaks down and falls to the bottom of the cliff. The debris, which accumulates at the foot of the cliff, forms a moderate slope and a stable cliff profile, which prevents continuation of the erosion process. This does not last for long, because sea waves remove the debris from the foot of the cliff leaving it with a precipitous slope and vulnerable to further erosion. The magnitude of the landslide or rock fall event determines, to a certain degree, the frequency of the event. The larger the event, the less likely another landslide or rock fall will occur at the same point in the near future. Losses of soil and rill development at the cliff slopes are a result of runoff action. The wind action has an effect on the erosion of the coastal cliff by blowing the loose sand from Kurkar and Hamra layers. The main factors influencing the changes (retreat or forward movement) of the base of the cliff are: the rock strength at the base of the cliff, and the ability of the waves to reach the base of the cliff and erode or sweep away material. Sea waves break upon the base of the cliff only a few days during the year. The cliff base is protected by the Kurkar Beit- Yanai rocks, which fell from the top of the cliff. During the winter the beach profile is relatively lower and flatter than in the summer, with a difference of more then 120 cm. Therefore, it is in the winter that the sea waves have a greater ability to erode and sweep away material from the base of the cliff. The rock, debris fall and slides occur during the winter month, as a result of rainfall. It was found that when a rainstorm is smaller than 10 mm the probability of a rock or debris fall event are nil. The probability of rock, debris fall and/or slide increases with the amount and intensity of the rain. During a rainstorm of over 90 mm, the probability of a rock, debris fall and/or slide event is 100 percent. In the study area the main cause of the coastal cliff retreat is the rain. Sea waves have a secondary role in the cliff retreat, mainly that of sediment removal from the cliff base. Without the sediment removal from the cliff base, the cliff would reach a stable slope and retreat process would slow down or eventually stop. The average retreat of the coastal cliff in the study area during the five-year study was 24 cm/year.
DE: 1810 Debris flow and landslides
DE: 1826 Geomorphology: hillslope (1625)
DE: 1843 Land/atmosphere interactions (1218, 1631, 3322)
DE: 4217 Coastal processes
SC: Hydrology [H]
MN: 2007 Fall Meeting