The Four Phases Of San Diego

As the crust moves away from the volcanoes and cools and becomes less dense and breaks up.

The forming of the geologic features go way back to starting with the beginning of North America millions of years ago. The land that is now known as Eastern California, was covered by a shallow sea. North America was slowly being pushed westward and oceanic crust was being pushed onto the side and being pulled underneath the continent. After continuous repetition, this accretionary wedge formed. This is when some of the crust pushes up onto the edge of the

Starting with the subduction of the oceanic plate which is being dragged beneath the North American Plate. The weight of the water on the oceanic plates increases the density of the oceanic crust to the point where it get snagged underneath the continental crust. After years of being dragged under the North American plate, the Pacific plate fills with high amounts energy and tension to then

Plate tectonics is the theory that the Earth's crust is divided into a number of plates that move because they float on the asthenosphere. Plate tectonics are moved by convection loops driven by geothermal activity. High temperatures inside Earth causes magma to rise into the asthenosphere and eventually reach the base of the Earth's crust. The magma spreads horizontally and cool. The cooling magma moves parts of the crust, creating mountains (Arbogast 290). There are three types of mountains associate with plate tectonics and they are volcanic, fold and block mountains. These are formed as "compressional forces, isostatic uplift and intrusion of igneous matter forces rock upward" (Williams). Volcanic mountains are formed when a tectonic plate

The Purisima Formation is extensively allocated “in central California from coastal exposures at Point Reyes in Marin County to more extensive exposures in the Santa Cruz Mountains from the coast in San Mateo and Santa Cruz Counties inland to the San Andreas Fault.” These scattered visible rock formations are part of the Purisima Formation because they all share a few specific characteristics: They all have interbedded mudstone, siltstones, and very fine-grained sandstones, with abundant shell debris. The Purisima formation was created “about 3 to 7 million years ago during the late Miocene and the Pliocene through a 4 million year period of deposition: The deposited rocks record a shift from deeper offshore conditions (primarily siltstone

Some scientists know that tectonic plates have moved over time because of California’s changes over time. Scientists have provided us with the evidence in multiple ways.

Following the end of Laramide crustal shortening and Palaeogene magmatism, the initiation of the development of the Rio Grande rift occurred between 31-28 million years ago in southern New Mexico (Berglund et al., 2012).. This rifting propagated northward to northern New Mexico (27-25 million years ago) and Colorado (27-26 Million years ago) (Crow, et.al., 2011). Early crustal extension involved low-angle faulting that formed broad basins and predates magmatism at the rift axis. This early- phase development of the Rio Grande rift lasted for 10 to 12 million years and was followed by a lull in volcanic activity between 17 and 14 Million years ago. This period of quiescence is apparent throughout the whole of the western USA, and it marks a change from volcanism that was dominated by calc-alkaline rhyolites and andesites to bimodal assemblages of basalt and rhyolite. It also marks a change in direction of crustal extension from WSW-ENE to E-W, that was accompanied by a decrease in the width of the zone of

The San Andreas fault in California is a transform boundary which means the tectonic plates grind against each other slowly building up tension through friction then one day they’ll slip causing an earthquake to occur.

Consecutively, the Taconic and Acadian mountain building occurrences took place, pressing and adding new land to the margin of North America. Although Acadian orogeny was a bigger mountain building event as compared to other periods’ events, around 250 to 300 million years ago during the Pennsylvanian and Permian periods, the ultimate mountain building event took place as ancestral North America collided with Ancestral Africa which had already joined the continents as Gondwana. As a result of this collision, the central and southern Appalachians were created. Sediment from the Iapetus ocean basin and the continental shelf and slope of North America was pushed upwards and pressed along with the crust; this mountain building event has been known as the Alleghenian Orogeny. However the Acadian orogeny primarily formed the northern Appalachian Mountains, the Alleghenian orogeny did the ultimate pressing to the margin of the continent which form today’s Appalachian Mountains. The Alleghenian mountain building events, just like other mountain building events, deformed, folded, uplifted, faulted, introduced, and pressed the crust of the Easter margin of North America. The affected rocks are comprised of sediments deposited in the inland ocean throughout the period of Paleozoic. They also include Iapetus and Avalon rocks; these rocks were added to North America from the Ordovician through the Devonian. In the meantime, as the Appalachian basin was filled with sediment produced as a result of eroding Appalachian Mountains, the inland ocean that existed west of the Taconic and Acadian Mountains started to recede slowly. The collision resulted in the rocks along the eastern margin getting compressed westward similar to a collapsing telescope. Crust slices were also pushed westward along faults such as the Brevard Zone that runs alongside the eastern edge of

In the east-facing subduction zone, a thrust belt developed as an accretionary prism, and the trench retreated within the subduction zone (slab-rollback) caused the thrust to migrate toward the continental margin. As a result, Havallah basin formed within an enlarging extensional region to the west of the trench and thrust belt. So how does slab rollback work? The slab rollback occurs when an older oceanic crust, which may lose heat by thermal contraction or another reason; thus becomes colder and denser than other slabs, then subducting at a steep angle. The slab rollback may pull the upper plate, as the colder slab collapses into the asthenosphere; it can roll back through the mantle. As a result it causes an extension in the overlying plate (example an enlarged extensional region in the Havallah basin) and possibly backarc spreading. Havallah sedimentation began during the emplacement of the allochthon, in an extending region to the west. Low grade rocks formed in the Osgood Mountains were exposed by tectonic unroofing during extension and unconformably overlain by post tectonic Pennsylvanian sedimentary rocks. In the hanging wall of the antler subduction system, arc volcanic that may have been erupted near or within the backarc extension, were extended and subside during or shortly after

The first part of this process is to be believed to be the separation and rifting of an older continent. The continued widening

Dr. Jackie Langille of the department of Environmental Studies at UNC-Asheville spoke today on the possibility of the formation of a new fault boundary between the Pacific and North American Tectonic plates. Currently, the San Andreas Fault is considered the primary location of fault slip, the movement of two plates past each other, between these two plates, however, Langille believes that the amount of fault slip occurring there may be decreasing as tectonic activity increases further inland. When she began this study, she hypothesized that Walker Lane, a recently discovered site of possible fault activity in Nevada, has been slowly increasing amount of fault slip that occurs there over time, and accounts for more and more of the tectonic activity between the Pacific and North American plates each year, and that the San Andreas fault is slowly becoming inactive. The implications of a shift in tectonic activity could alter the global map. As the two plates slide past each other, they cause the land, ocean and other crust formations they

While Earth’s plates continuously create new ocean floor and continental land, but also makes it disappear. At divergent plate boundaries, the plates push together and magma rises to the surface. When this magma cools it creates new plate material. Scientists know this because the seafloor near these volcanoes is the youngest seafloor in the ocean. At convergent subduction plate boundaries the plates subduct, and one plate goes into the Earth. As this plate gets lower it slowly starts to melt and becomes magma. Scientists know that the plate is destroyed because of the Law of Conservation of Matter, which states that matter cannot be created or destroyed, only recycled. As the new plate material is created,

Geologists trust that the world 's hull is isolated into huge plates that fit together like the bits of a mammoth jigsaw riddle. These plates are thought to move persistently, for the most part on a level plane. As per geologic hypothesis, the plates meet in no less than three ways, and two of these are imperative to our story: subduction zones (where one plate moves underneath the other), and change limits (where the two plates grind past each other). At some point around sixty million years prior, when our video starts, the lighter-weight North American Plate started abrogating or subducting the denser Farallon plate, and as it did, its external edge went about as a bulldozer, gathering up

In the fall of 1989 on the seventeenth day of October at 5:04pm Pacific time, there was a fateful earthquake that claimed sixty three lives, created almost four thousand reported casualties and caused more than six billion in damages destroying many homes and businesses throughout the state of California. The epicenter of the earthquake originated in the Loma Prieta Mountains just outside of Santa Cruz, California. The fault that the earthquake occurred on is the San Andreas Fault system. Which has spider webs spanning approximately forty miles wide and runs north-west and south-east for over eight-hundred miles through California. This fault line forms the boundary of the Pacific plate and the North American Plate. The San Andreas