Patrick - Science 12.16.13

Front 1

Explain how weathering and erosion affect mountains over millions of years

Back 1

Weathering breaks or dissolves the rock. Erosion transports the resultant sediment to another location.
Together, this leads to a very gradual reduction in the elevation of a mountain.

Front 2

Distinguish between types of mechanical and chemical weathering

Back 2

Mechanical weathering is the physical breakdown of rocks into smaller particles by abrasion, frost wedging, etc. Chemical weathering is the chemical alterationof minerals in the rock due to the action of water, oxygen and acids in the soil, and dissolution of carbonates. The minerals actually react with the acid ground-water to form other minerals, and some go into solution. Minerals like feldspar break down into clay minerals and so on. Mechanical weathering is favoured by cold dry climates, and chemical weathering is favoured by warm, humid climates.

Front 3

Explain the risks involved with living near a river

Back 3

A river is a stream of water that flows through a "channel" (or passage) in the surface of the ground. The passage where the river flows is called the riverbed and the earth on each side is called a riverbank. A river begins on high ground or in hills or mountains and flows down from the high ground to the lower ground, because of gravity. A river begins as a small stream and gets bigger, the farther that it flows.
The start of a river is called its "source" or its "headwaters". The part of the river that is near the source is called a "young" or "youthful river".[1] A young river is often in a V-shaped river bed, and flows quickly downhill over stones, and around big rocks. Young rivers often have lots of small waterfalls and rapids.
The source of a river may be a spring, often on a hill, mountain, glacier, or another high place. A spring is water that flows out from under the ground.
The middle part of a river is called a "mature river". A mature river makes a riverbed that is U-shaped. It might be very deep and run fast. It sweeps over small rocks and boulders, and makes big turns around hills and mountains. It is much wider than a "young river", but not as wide as an "old river". To cross over a mature river, people use bridges. Many cities and towns are built on the banks of mature rivers. Many farms that keep animals such as dairy cows, horses and sheep are along mature rivers because the animals can drink from the river every day.
A river usually ends by flowing into an ocean, a lake or a bigger river. The place where the river flows out into a bigger body of water is called the "mouth" of the river.

As a river flows towards its mouth, the countryside around the river often changes from hilly to flat. As it flows over the flat land the river becomes wider and slower. A wide slow river is called an "old river". An "old river" often floods across the land after there is lots of rain at the "headwaters". An "old river" slowly builds up its banks on either side; the high banks are called "levees". An old river often "meanders" (twists and turns), and sometimes, after a flood, it leaves lakes behind which are called "ox-bows" or "billabongs". Old rivers are the most useful type of river for growing crops. Corn, rice, fruit, cotton, hay, tobacco and sugar are some of the crops that are grown near old rivers.

The shape of the mouth depends on the conditions of the sea where it flows. If there is a strong tide where the river meets the sea, the river forms an estuary. An estuary is a wide, funnel-like mouth of the river. The fresh water of the river mixes slowly with the salt water, becoming brackish water – a "break" between fresh and salty water. Many kinds of fish, clams, mollusks and other sealife live at estuaries. Many of the world's largest cities and harbours are at estuaries.

Where a river flows out to the sea, it sometimes flows very slowly through sandy or muddy land, making lots of little islands as it flows. The main stream of the river gets broken into many parts that spread out into a triangle shape like the Greek letter "Delta". When this happens, it is called the "delta" of the river. Deltas are often places that are not good for towns or farms but are very good for birds and other wildlife and fishing. Deltas are often made into wildlife reserves. Not all rivers have deltas
A river flowing in its channel is a source of energy which acts on the river channel to change its shape and form. In 1757, the German hydrologist Albert Brahms empirically observed that the submerged weight of objects that may be carried away by a river is proportional to the sixth power of the river flow speed.[8] This formulation is also sometimes called Airy's law.[9] Thus, if the speed of flow is doubled, the flow would dislodge objects with 64 times as much submerged weight. In mountainous torrential zones this can be seen as erosion channels through hard rocks and the creation of sands and gravels from the destruction of larger rocks. In U-shaped glaciated valleys, the subsequent[clarification needed] river valley can often easily be identified by the V-shaped channel that it has carved. In the middle reaches where a river flows over flatter land, meanders may form through erosion of the river banks and deposition on the inside of bends. Sometimes the river will cut off a loop, shortening the channel and forming an oxbow lake or billabong. Rivers that carry large amounts of sediment may develop conspicuous deltas at their mouths. Rivers whose mouths are in saline tidal waters may form estuaries.