Block Mountain and Rift Valley When the land

Block Mountain and Rift Valley • When the land between two parallel faults is pushed up, a landform called a block mountain (B) is formed. The process can also result in a block of land being pushed down, forming a rift valley (A). A B

Wearing down the land • Just as the land is constantly being built up; it is also constantly being worn away. • The process of this wearing away of the land is referred to as Denudation and it is composed of two components: – Weathering – Erosion • To begin with, we shall look at weathering.

Wearing down the land • The process of weathering helps wear down the land through two methods: – physical weathering : The process whereby atmospheric forces and tectonic activity physically shape the land – Chemical weathering: The process whereby chemical reactions of minerals, elements and compounds causes changes in structures on the earth.

The mechanical processes by which physical weathering occurs. • Frost Fracture: – Fluctuations in temperatures above and below freezing cause rocks to become brittle and break. – It also causes continual expansion and contraction which weakens landforms and eventually allows for breakage. – In addition, water can get into cracks and crevices, and contribute to frost fracture through its own cycle of freezing and thawing.

The mechanical processes by which physical weathering occurs. • Exfoliation: Sometimes, rock surfaces tend to fracture along naturally occurring lines of construction (This is especially true of sedimentary rock formations).

The main interactions that result in chemical weathering • Solution: – Usually rainwater is associated with this process, absorbing carbon dioxide and possibly other elements from the atmosphere. – The additions of these chemicals transforms the rain water into a weak carbonic acid, which in turn can react with minerals in rocks to form new soluble compounds.

The main interactions that result in chemical weathering • Hydrolysis: – Carbonic acid reacts with a silicate and forms a new soft clay mineral. The silicate’s potassium, sodium, and magnesium are carried away in solution. The soft clay left behind ultimately decays into soil or mineral deposits.

The main interactions that result in chemical weathering • Oxidation: – This involves the reaction of metallic minerals in rocks to oxygen and water. – The result of the reaction is a new mineral called an oxide. – Oxidation often creates softer minerals that weaken the rock structure which may eventually crumble and be eroded away.

Erosion • Another type of denudation, it includes the breakdown of rocks and landforms, and their transportation to other locales. • There are several different agents, or mediums, that contribute to the process of erosion. One of the most important of these is water in motion.

How running water acts as an agent of erosion • The earth’s running water can be thought of as a natural plumbing system: – Through the force of gravity, surplus water is “channeled” from high ground to lower ground, always attempting to reach the lowest ground, thereby being deposited in aquifers, ponds, lakes and eventually the ocean. • The “pipes” in this plumbing system have established themselves over the billions of years that rain has been falling on the earth. – They are continually constructing and demolishing themselves in an evolutionary process that is subject to the forces that are created by the running water itself. – Today we call these “pipes” river systems.