An example of this is at Maori Bay. Coastal Erosion operates at different rates and different times. Limestone rock is eroded slower than sedimentary rock. The cliff at Muriwai made of sedimentary rock was eroded back to expose 'Fisherman's Rock' - the shore platform which, made of limestone -- tended to erode back slower than the cliff. The types of wave erosion that caused this are - Hydraulic Action, when waves hit the cliff, air is forced into cracks, and then as the wave retreats this air expands explosively.
Sedimentary rocks are the rocks formed from compaction and cementation of fragments of pre-existing rocks called crystals. Exogenic processes such as weathering and erosion influence the formation of sedimentary rocks. This processes supply the materials (sediments), responsible for the formation of sedimentary rocks. Weathered materials are transported by the agents of denudation such as water, wind and ice; then are deposited in low altitude areas. The accumulated materials are compacted as results of increasing pressure, finally the material are cemented following the precipitation of silica, calcium carbonate or iron oxide between particles.
Sand can be talked about as sediment when it is together with silt, gravel, and clay. (3) But on top of that basic definition, one should know what makes up sand, the ways sand is distributed, and about Amelia Island itself. As told earlier, sand is formed from worn rock. Those rocks are the sedimentary, metamorphic, or igneous rocks. A sedimentary rock is made up of chemical, mechanical, or organic sediment.
The descending in the subduction zone begins cold. As it descends heat increases because of the geothermal gradient and friction of subduction and heat lead to Fractional Melting . The initial melt may be mafic,but evolves through time to intermediate (Diorite/Andesite) and felsic (Plagiogranite/Rhyolite) rocks. Step 3- Generation of high P/high T ecolgite by descent of unmelted oceanic lithosphere which usually takes place above the subduction zone. The oceanic lithosphere which descend into the mantle has now been fractionated twice, once at the oceanic rift center, and now a second time along the subduction zone.
Overlying rock contributes to high pressure. Minerals in the rock align in layers when the pressure is stronger in one direction. This process can be speeded up with the help of hot liquids and gases in the deep rocks. The two types of local metamorphism (contact and deformational) are also affected by certain factors. Contact metamorphism occurs when hot magma heats and changes rock.
This section will discuss the geological history of the area for each lithological formation, as well as identify the main structures and what these were caused by. The Millstone Grit at its base has an unconformity formed by uplift and folding of a northerly landmass. It has a thick series of quartzitic sandstones formed from weathering of an earlier landscape. There are several movements due to subsidence, which can be seen in the Millstone Grit through the basal grits. Following the Millstone Grit the coal measures were deposited with a gradual change due to increasing sea levels.
“Earthquakes occur when tension stored in rocks suddenly releases” (Vogt 12). Faults occur at these places where rocks on either side of the crack have moved. Oceans are very common places for major tectonic plates to shift. When two plates separate, new oceanic crust is made near the fault as magma rises and eventually sets on the sea floor. If the plates on either side of the fault continue to spread then the ocean slowly becomes larger in width.
First ocean waves, rivers, glaciers, wind or landslides transport loose, solid particles from weathering and erosion of preexisting rock. The particles are named sediment (Rocks of Idaho). Next the loose sediment is converted into sedimentary rock in compaction, cementation, and recrystallization. Compaction is when the air and water is pushed out of the bottom layer of sediment as more layers build up and press down on it. Cementation is when the sediment is cemented together with natural cements like calcite and silica.
Most of the rock in the area was formed during the Jurassic period approximately 150 million years ago. Most of the rock formed in this period was limestone and shale. Lias is the most commonly found shale in this area, a soft, reddish coloured rock. Beaches are the most common of the four depositional features. They are created by deposited material from breaking waves; the constructive action is mainly effected by the swash.
A large portion of the granite is made of small crystals of orthoclase feldspar which give the rock the pink or reddish colour. Other minerals present are quartz (usually gray). albite feldspar (white) and either white mica (muscovite) or black mica (biotite). The word granite means grain-rock, it weathers, and it crumbles into loose grains. 7.