1. Unit One Land And Water Forms
World Geography 3202
Unit One
Land And Water Forms

2. Introduction
Unit 1 introduces You to the concept that the earth’s surface is shaped by building-up and wearing away forces.
The unit will help You to examine the constituent parts of the physical environment, forces that created them, patterns in their distribution, and how they influence selected human activities.

3. Patterns in the location of landforms on the earth’s surface
Q#1 What category of landforms would be reflected in this type of diagram
Q#2 What pattern can be seen from the diagram of landforms illustrated here?

4. Relief map of North America
Q#1 How would you describe the distribution of landforms illustrated in this map?
Q#2 What type of landforms can you identify on this map?
Q#3 Where in the Americas are you most likely to encounter:
Mountains
Large Lakes
Plains and Plateaus
Large Rivers
River Deltas

5. Questions for Review Define the term topography.
Differentiate among the terms hill and mountain, and plain and plateau.
Identify: seismology; minerals; rocks; compounds; elements; Igneous rocks; Sedimentary rocks; metamorphic rocks; Valleys;
Describe the distribution of these landforms over the earth’s surface

6. How did this distribution come about?
The earth’s landforms are never static: That is to say, they are constantly in a state of change due to forces at work that both wear down the land, as well as build up and shape the land.
First, we are going to look at forces that build up and shape landforms,….

7. Forces that shape the earth’s land formations
The face of the earth is shaped by tectonic activity.
Tectonic activity can be described as the movement of the earth’s crust, or “plates” as a result of the pull of gravity; convection currents, or the circulating movement of fluid rocky material in the mantle; and thermal plumes, or vertical columns of molten rocky material in the mantle.

8. Crustal Movement Under the ocean

9. How Plate Tectonics Explains the shaping of landforms
The theory of plate tectonics was formulated during the early 1960s, and it revolutionized the field of geology.
Scientists have successfully used it to explain many geological events, such as earthquakes and volcanic eruptions as well as mountain building and the formation of the oceans and continents.

10. What are Tectonic Plates?
Tectonic plates are made of either oceanic or continental crust and the very top part of the mantle, a layer of rock inside the earth.
This crust and upper mantle form what is called the lithosphere.
Under the lithosphere lies a fluid rock layer called the asthenosphere.
The rocks in the asthenosphere move in a fluid manner because of the high temperatures and pressures found there.
Tectonic plates are able to float upon the fluid asthenosphere because they are made of rigid lithosphere.

11. Layers Of the Earth 1. Lithosphere 2. Mantle 3. Outer Core
4. Inner Core

12. How compressional forces are caused.
Compressional / Destructive (subduction zones) plate boundaries occur when an oceanic plate is forced under (or subducts) a continental plate
What do you think could be the result of this type of force?

13. Compression at Work:

14. How tensional forces are caused
Tensional / Constructive (divergent ) plate boundaries occur when two plates move away from each other
What do you think could be the result of this type of force?

15. Relate selected plate movements to compressional and tensional forces
An earthquake is a sudden movement of the earth's surface.
Earthquakes are caused by the movement of the earth's tectonic plates.
Earthquakes occur where the earth's plates meet along plate boundaries

16. An example of the cause of an Earthquake
For example as two plates move towards each other, one can be pushed down under the other one into the mantle.
If this plate gets stuck it causes a lot of pressure on surrounding rocks.
When this pressure is released it produces shock waves. These are called seismic waves. This is an earthquake.
The waves spread out from the point where the earthquake started - the focus. More damage is done near the focus.
The point on the earth's surface directly above the focus is the epicentre.

18. Volcanoes
A volcano is a conical hill or mountain formed by material from the mantle being forced through an opening or vent in the Earth's crust. Volcanoes are found in three states - extinct, dormant and active.
An extinct volcano will never erupt again.
A dormant volcano has not erupted in 2000 years.
An active volcano has erupted recently and is likely to erupt again.
Volcanoes are found along destructive (subducting) plate boundaries, constructive (divergent) plate boundaries and at hot spots in the earth's surface.

20. What are the three main volcanoes?
There are three main types of volcano - composite or strato, shield and Ash and Cinder.
Composite volcanoes, sometimes known as strato volcanoes, are between the steep sided ash and cinder cones and the low-lying shield cones.
They are formed from layers of ash and [lava] flows. When composite volcanoes erupt they are sometimes explosive and sometimes less violent.
Shield Shield volcanoes have gently sloping sides and are formed from layers of lava. Eruptions are typically non-explosive. Shield volcanoes produce fast flowing fluid [lava] that can flow for many miles.  
Ash and Cinder volcanoes are typically violent and destructive, characterized by narrow tall cones.

21. Pacific Ring of Fire
The "Ring of Fire" is an arc stretching from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands of Alaska, and south along the coast of North and South America.
It is composed over 75% of the world's active and dormant volcanoes.
This huge ring of volcanic and seismic (earthquake) activity was noticed and described before the invention of the theory of plate tectonics theory.
We now know that the Ring of Fire is located at the borders of the Pacific Plate and other major tectonic plates.

22. Around the Ring of Fire, the Pacific Plate is colliding with and sliding underneath other plates.
This process is known as subduction and the volcanically and seismically active area nearby is known as a subduction zone.
There is a tremendous amount of energy created by these plates and they easily melt rock into magma, which rises to the surface as lava and forms volcanoes.

24. Fold Mountains
Fold mountains are mountains formed from the folding of the earth's crust.
Fold mountains are formed when two plates move together (a compressional plate margin).
This can be where two continental plates move towards each other or a continental and an oceanic plate.
The movement of the two plates forces sedimentary rocks upwards into a series of folds.
Fold mountains are usually formed from sedimentary rocks and are usually found along the edges continents. This is because the thickest deposits of sedimentary rock generally accumulate along the edges of continents.
When plates and the continents riding on them collide, the accumulated layers of rock crumple and fold like a tablecloth that is pushed across a table.

25. Diagram of fold mountain being formed

26. anticline and syncline
Simple folding forms are upwardly or downwardly pushed layers of the earth that resemble waves.
The Peak of a wave –like form is called the Anticline
The Trough of a wave-like structure is called the Syncline

27. How tensional forces create a normal fault
When plates are pressed against each other, intense pressure or the brittleness of the rocks involved may cause the rocks to fracture or break apart. This is called Faulting.
If a plate on one side of a fault drops down lower than the plate on the other side, the result is a normal fault

28. Diagram of a normal fault

29. reverse fault
If simple rock layers push against each other instead of pulling away, one block may be pushed up over the other, resulting in a Reverse Fault

30. Overthrust Fault
If a plate that suffers a Reverse Fault has already undergone folding, and its folded layers are then pushed up and thrust over layers on the fault’s other side, an overthrust fault occurs.

31. 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

32. 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.

33. 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.

34. 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.

35. 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).

36. 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.

37. 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.

38. 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.

39. 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.

40. 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 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.

41. The life cycle of a river
The life cycle of a river helps explain how it acts as an agent of erosion.
It should be obvious that the force of running water will create erosion in the first place. Running water will physically move objects and “carve” or erode rock formations if the motion and volume of water is continual. In the “youth” stage of river cycle, a river does just this: It carves out a path to it’s final destination over rock formations, wearing away the land as it does so.

42. The two ways in which water acts as an agent of erosion
Rivers concentrate their energy to erode both vertically and laterally.
Vertical Erosion: A river erodes the bottom of its channel, and it is the chief from of erosion for a youthful river, usually formed at higher elevations.
Lateral Erosion: Gives older rivers their meandering shape, as a river flows faster along one bank, it erodes that bank. Conversely, as the water loses momentum on the opposite curve, it deposits sediment and loose materials on that bank, eventually filling it in.

43. Which Bank Reflects the erosion process at X Y ?

44. Youth In it’s youthful stage, a river is characterized by:
A rapid flow
Steep valleys, waterfalls
Narrow, straight passages

45. The life cycle of a river
Gradually, the force of the youthful river will erode away most of the high ground around the river.
Subject to gravity, the water in the river will have to slow down, as a result of a gentler slope and a flat land surface.
At this point, a river comes to be known as mature

46. Characteristics of a mature river
Many well-developed Tributaries
Broad flat valley with a well developed flood plain

47. The life cycle of a river
A mature river represents roughly an equilibrium between erosion and deposition:
Its ability to erode material further and it’s ability to deposit material at the basin of the river are roughly equal
As the river ages further, the land around the river becomes extremely flat.
When this occurs, the river slows, loses momentum, and begins to deposit material more than it erodes.
At this point a river is said to be old

48. Characteristics of an old river
Very elaborate and meandering courses
Swampy areas
Oxbow Lakes

49. Diagram of the life cycle of rivers

50. Rivers as agents of Deposition
The material that a river erodes, is carried by the water to its end destination, be that a pond, lake, or the ocean.
This material is deposited in various locales by the running water as it loses its forward momentum, and the force of gravity causes the sediment to settle.
As a result we can say that rivers are also agents of deposition, creating various landforms.

51. How deltas are formed
Heaviest particles are unloaded first as a river loses momentum, closest to shore, forming a thick layer of sediment.
Smaller particles are dropped further out leaving a thin layer.
This process is repeated over and over again, until a delta is formed.

52. Types of deltas.
Arcuate Deltas: Are a curved shape, like a bow, or a bird’s foot

53. Types of deltas.
Digitate Delatas: Are long and narrow, in the shape of a “finger”.

54. Types of deltas.
Estuarine Deltas: In estuaries, fresh river water mixes with sea water. Sediment is deposited from both river outflow, and seawater inflow. At low tides, the deposited materials can be seen in the form of Estuarine Deltas.

55. How moving ice acts as an agent of erosion and deposition
Today, a tenth of the earth’s surface is covered in ice.
Glaciers are a major agent of erosion on the earth’s surface. These glaciers are constantly receding and growing, and it is this growing and receding that gives glaciers their ability to erode and build up the earth.

56. Glaciers
The glaciers that denude the earth’s surface today, are of two types:
Alpine Glaciers: Form in high mountain valleys above the snow line.
Continental Glaciers: Are large ice sheets covering major portions of entire continental land areas.

57. How Glaciers erode
Glaciers erode in three ways as they move with their ice flowing outward and downward.
First, glacial ice pushes loose material along the sides and in front, in a sort of bulldozing action.
Second, as the ice continues to move and has embedded sediment in it, the ice and material scratch and gouge out new material from a new surface.
Third, glacial ice can freeze to underlying blocks of rock surfaces. As the ice continues to move, it may actually pull out blocks of material.

58. Alpine Glaciation
Alpine glaciers are responsible for many of the features we can recognize on large mountain tops today.

59. Features of Alpine Glaciation

60. Continental Glaciers

61. Erosion Through Wave Action
Running water acts as an agent of erosion and deposition:
As we have seen, running water (usually illustrated through the life cycle of a river) can have a dramatic effect on a given landform.
There is a second way in which water acts as an agent of erosion, and that is through wave action.

62. Wave Erosion
Lakes and oceans derive their ability to erode from the wind.
When wind drags on the water’s surface, it transfers its energy through the water as friction. The result of this energy transfer is a wave.
These waves then strike coastal areas causing different erosion effects

63. Wave Erosion
The ways in which waves can change a coastline depend on how the coastline has been formed:
Some coastlines are a result of rising sea levels and some are a result of declining sea levels.
Sometimes glaciers recede and the land rebounds to form a coastline. In a similar process, sometimes sea levels fall, and a coastline emerges.

64. Emergent Coastline
Are the result of rising land levels (and falling sea/ice levels).

65. Submergent Coastline
This type of coastline results from rising sea levels and is illustrated in stages below: