Geology; Pacific shore – Mendocino Ecological Staircase

	Marine geology

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"This turn revealed a grand & glorious coast to behold." Mendocino, December, 2005. A marine terrace above an inlet of the Little River, on the edge of the Mendocino escarpment, Ca. Objectives: To understand generally how the geology of the western USA shaped the coastal geography of Northern California. To precisely understand the origins and significance of the geological features of Jug Handle State Preserve and the landscape elements of the Mendocino ecological staircase. To appreciate the role of "edaphic" factors such as wind, soil, water, and tectonic forces in the shaping of coastal vegetation. To recognize the variety of neighborhoods and the need for protecting rare and scientifically valuable vegetational associations or biotic communities in the coastal zone. Begin to visualize how the earth's forces move surface rocks. Visualize The earth moves in three ways -- also! back and forth horizontally up and down vertically in response to tectonic plates which (See: three boundary patterns) rise up, go underneath, or slip past one another. 1. Horizontally this island moves in the prevailing currents that move waves that move its sands: 2. vertically and horizontally over time the surface features move. Plate Tectonics and continental drift theory Defining terms Plate tectonics, the concept that the Earth's surface is fractured into several internally coherent, but different blocks of either basaltic or pyroclastic and sedimentary terrains. fracture zones are those areas of a large or small plate that --as a block of that plate-- break or slide apart from the adjoining mass at a different rate of speed than the entirety of the parent plate. transform faults are associated with slippage and fracturing along a boundary, where neither one plate nor another --adjacent-- plate has any discernible vertical movement; and instead the forces push each block past the other. The stress of this lateral collision creates fault systems where seismic activity and earthquakes periodically relieve the stresses of one mass of rock grinding past another. subduct, subduction: the term for one plate slipping under *[sub], or going [duct] down, or moving beneath another. Convergent plate boundaries* are a characterized by subduction zones that are related to island arcs or hot spot activity where the melting of the plate going under an adjacent plates brings molten rock to, at, near or over the surface features of the landscape. Divergent plate boundaries are areas associated with spreading, usually sea floor spreading as in the East Pacific Rise, the Mid Atlantic Ridge, or as in the case of Iceland and the Great Rift Valley of East Africa these areas where plate boundaries are separating can occur over land. In these regions where plates separate (as opposed to coming together or converging) are forces that release magma from below the surface and extrude lava. As the lava solidifies on either side of the rift each side of the fracture moves apart from the other side of the magma well. This existence of an ever growing displacement of lava is the primary cause for the movement of one massive plate or block away from another at differential rates of divergence (different speeds at which the plates move out and away from one another). Edge of the Sea, an overview of concepts, themes and terms. California foothills and the American River which drains the western Sierras. Authority is: John McPhee, Assembling California. California's coastal geology Essay Coasts can be influenced by land, air and water in various ways, but the Western US along the Pacific coast is affected by tectonic, or geologically active forces, as much or even more so than other influences such as weathering or sea level rise and tides. Very similar to Japan, this is a seismically active area associated with the impacts of the "ring of fire" a series of volcanoes that stretch along the Pacific Ocean rim from Indonesia, to the Philippines, up to Japan and Kamchatka in Russia, over to the Aleutian Islands and eastern Alaska, then down the coastal and Cascade ranges to Baja, Mexico and on down along the Andes of South America. The earth's crust is restless in the sense of geological time and the Pacific area is a vast block of basalt that is fractured in many places. Those fracture zones, called transform faults --running laterally to one another and perpendicular to the California coast-- are numerous. But two very important fractures zones come ashore at Cape Mendocino and Point Conception forming among other terrain features, the Great Central Valley of California. More recently (the last 15 million years) the movement at an angle nearly perpendicular to these lateral transform fault, fractures has caused the deformation of the Pacific Coast by the San Andreas fault system south of Cape Mendocino. The Channel Islands of Southern California and Baja are remnant of down faulted marine terraces that have sunk below the sea due to both tectonic forces and the slow rise in sea level in the past 10,000 years since the end of the last ice age. J. Siry *previous essay* *next essay* Sources Authors Guide West coast geology Marshes of the Ocean Shore Edge of the Sea contents Edges of the Seas, an overview of concepts, themes and terms. Date: February 10, 2008