111-19 - GY 111 Lecture Notes D. Haywick (2008-09) 1 GY 111...

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GY 111 Lecture Notes D. Haywick (2008-09) 1 GY 111 Lecture Note Series Sedimentary Environments 2: Rivers and Deltas Lecture Goals A) Rivers and Deltas (types) B) Water Flow and sedimentation in river/deltas C) Sedimentary rock types Reference: Press et al., 2004, Chapter 7; Grotzinger et al., 2007, Chapter 18, p 27-431; 436-442 GY 111 Lab manual Chapter 3 A) Rivers and Deltas (types) Before we get too far, it is probably best to state right away that rivers and deltas are separate depositional systems and should be discussed individually. We are combining them here because of time constraints. That being said, there are legitimate reasons to consider them together in a GY 111 class as rivers and deltas are related. Rivers are channels that contain water that is flowing down hill. The flowing water is carrying sediment and that sediment is eventually transported to large standing bodies of water like lakes and where we live, the oceans. When the flowing water of the river channel meets the sea, it immediately slows and this results in a tremendous amount of sediment deposition. The deposit that forms can be 100's of km 2 in extent and is called a delta ( see picture to left of the Mississippi Delta) Both rivers and deltas contain channels and in both river and delta systems, the channels come in different sizes and shapes. Rivers are considered to be the largest of the channels. Creeks, streams and ditches are all smaller versions of rivers. For now, let's focus in on rivers. In Alabama, almost all rivers (streams and channels) contain water all the time. We live in a wet climate and the water that flows in channels largely comes from rainfall. In drier climates (e.g., the SW USA), streams periodically dry up. These ephemeral streams are common elements of arid regions and deserts around the word. Water may not flow through these streams all the time, but when it does flow (say after an infrequent major thunderstorm), it flows really fast. Many a camper has been swept away through these sudden surges. If the water flows over the banks of the river (it exceeds the carrying capacity of the stream), we say that the river has flooded . If the water rise and flooding event is quick (sometimes only a matter of minutes), it is called a flash flood . By the way, I should mention that while it is true that most streams in Alabama receive the majority of their water through rain fall (this is officially called runoff ), some of the water gets into channels through ground water . This process is especially common in arid regions and is one of the reasons why rivers like the Colorado contain water even after flowing hundreds of miles across deserts. Some of the water leaks into the channels through groundwater infiltration :
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This note was uploaded on 02/04/2012 for the course GLY 111 taught by Professor Haywick during the Fall '11 term at S. Alabama.

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111-19 - GY 111 Lecture Notes D. Haywick (2008-09) 1 GY 111...

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