Presentation on theme: "Waterfalls Glenn brookes Ryan hogg Jack forman. Introduction Waterfalls are found mainly in the upper stages of a river; they form a gorge when hard rock."— Presentation transcript:
Waterfalls Glenn brookes Ryan hogg Jack forman
Introduction Waterfalls are found mainly in the upper stages of a river; they form a gorge when hard rock is located above soft rock and over time erosion takes its cause.
Example – angel falls, Venezuela One of the world’s most renowned waterfalls is that of Angel Falls, Venezuela in South America. It is the world’s highest free-falling waterfall coming in at just under 1000m at 979m. It is situated in the river Churún; the name of the waterfall is so that in the native language it literally means THUNDER! It is located way out in the wilderness of Venezuela and getting there is not an easy task, involving a long flight from the town of Caracas and a trek to the top.
The process of a waterfall
Stage 1 - undercutting The undercutting of the waterfall is a simple process, it involves the rocks coming down from the waterfall; these then cut back into the soft rock at the base of the waterfall eroding it away – this is what is known as undercutting.
Stage 2 – overhang collapses This is connected to the first phase of a waterfall; continuous undercutting means that the hard rock that is found above the soft rock becomes un-supported so it just falls away moving the waterfall further back up the valley.
Stage 3 – plungepool develops The plungepool is found at the base of a waterfall; this is created again through a process of erosion; it is made by the sheer force of boulders falling from the waterfall and ‘plunging’ into the water below; eroding away the bed of the river.
Stage 4 – waterfall retreats back upstream This is linked to stage 2 of the process in the way that the main reason behind this is the fact that undercutting makes the overhang collapse thus moving the waterfall further back up the valley.
Stage 5 – steep, gorge-like valleys The valleys that waterfalls are found in become steep due to the fact that the undercutting erodes at an angle making the valley become fairly steep.
What is a V-shaped valley? V-shaped valleys are typically found in upland areas and are one on the earliest stages in a river’s journey towards the sea. A v- shaped valley earns its name from its distinctive shape, comprising of a wide top and narrow bottom in which the river may be found, with steep but sloping ‘shoulders’ or sides. V- shaped valleys are formed by a river eroding away at the rocks of a valley, slowly cutting a channel for itself into the rock. Formation of a valley often takes anything up to three million years, with the river wearing a channel sometimes half a mile into the rock. As the river erodes through rocks it will often encounter differing bands of sediment. Some of this sediment is worn away faster than others, and can result in the sides displaying a serrated appearance a shown in this photo of the Grand Canyon in the U.S state of Arizona. V-shaped valleys also often contain interlocking spurs of rock that cause the course of the river to meander in the valley itself. During a period of glaciations, a v-shaped valley may undergo subsequent erosion from an ice flow and become a U-shaped valley.
Some Pictures of V-shaped Valleys
How are Rapids formed? Rapids are stretches of fast-flowing water tumbling over a rocky-shallow riverbed. They are caused by different resistance among various rocks, that leads to sudden drops and rises in the river bed. That in turn causes instabilities in the flow of a rivers currents. They are formed when the water goes from one hard rock that resists the water's erosion to a softer rock that is easier eroded. The debris formed by the erosion breaks up the flow of the river, but are not big enough to form a waterfall. Over time, rapids are formed.
How they’re created Interlocking spurs Occur in the top part of a river course in upland areas. The water cannot erode the hard rock as easily as soft rock, so eventually the course of the river reflects this and ridges are produced when a river twists and turns around obstacles of harder rock on its downward path. The ridges interlock in a zipper like the teeth of the zip.
Case Study: R. Dane This is the R. Dane nr Macclesfield in Cheshire, near the Peak District National Park. The Rivers source is in the Pennine Hills, starting in a peat bog. The physical of the geography of the area gives ideal conditions for a river to start, with the bogs retaining water when it rains, but allowing it’s slow release over time. The image opposite shows an interlocking spurs (Small letter ‘S’) Source: ycle/dane/d_map.htm ycle/dane/d_map.htm