Physical Geography Unit 1 - Land and Water Forms Landform Patterns and Processes

THE STRUCTURE OF EARTH (p. 4) The earth can be divided into distinct structural zones (eg. Inner & Outer core) While features on the surface are easily observable, internal features have to be studied indirectly. – Seismology, the study of earthquakes and other earth movements, uses special instruments that allow seismologists to track earthquake waves through earth’s interior. – Computers are used to create visuals of distinct zones within the earth (each zone has its own density and temperature).

Zone/BoundaryThickness (diameter in km) Features Inner core2700 solid; composed mostly of iron, with lesser amounts of nickel; temperature of 4000 to 6000 ⁰C. Outer core2300 molten (liquid); composed mostly of iron and nickel; temperature above 4000 ⁰C. Mantle2900 divided into lower and upper layers; moderate density, largely solid except for upper km of upper layer, called the asthenosphere (this section is in a plastic state, sometimes acting like a liquid); made mostly of magnesium and iron silicates Mohorovicic Discontinuity — boundary between mantle and lithosphere, at which earthquake waves abruptly change speeds Lithosphere1-100 lowest density (solid and rigid); made up of the lightest elements and compounds (mostly magnesium, aluminum, and iron silicates such as granite); can be divided into two layers, one under ocean basins (sima) and one making up continents (sial); rocks of continents are also referred to as crust (crust is km thick)

The lithosphere is made up of two primary materials: Minerals: natural chemical compounds made up of a combination of elements. Over 2000 have been identified, but fewer than 30 are widely deposited in the earth’s crust. Rocks. Physical and chemical processed may be involved in the creation of three rock types. Igneous rock forms when magma or lava cools and hardens. This process may occur below the surface (intrusive) or on the surface (extrusive). Sedimentary rock forms when small particles merge and cement together. This often occurs when rivers transport pebbles, sand, and small fragments into lake or sea beds. The weight of upper layers causes compaction, cementing particles together. Metamorphic rock forms when already existing rock, under great heat and pressure, is transformed. The chemical composition of the rock is altered, creating new rock.

Earth has a variety of landforms resulting from billions of years of geologic change. This change occurs through wind, water, earthquake, and volcanic activity. Topography: the natural and human features of Earth’s surface. The most common topographical features of earth are: – Valleys: The lowest points on Earth’s surface (depressions in the crust) STRUCTURES ON EARTH’S SURFACE (p. 6) Type of ValleyCharacteristics V-shapeFormed by river erosion (fast moving). Flat-bottomFormed by river erosion (slow) U-shapeFormed by glacial erosion Rectangular with steep sides Formed by faulting or folding

– Plains: level tracts of land frequently found along coastal areas or at low elevations (e.g.: river valleys, flanks of mountains). Plains may have a gentle slope, but no local relief of more than 30m. – Plateaus: extensive, relatively flat upland areas that have been raised to higher elevations by the movement of Earth’s crust. Often found on the interior of continents. – Mountains and hills: areas of highest relief (difference in local land height). Mountains are > than 600m, while hills are < 300m. Often found in lineal chains (ranges) along the margins of continents. *Complete “Earth’s Surface: Topography Activity”* Type of PlainsCharacteristics AlluvialFormed by river action LacustrineWere once the beds, or bottom surfaces, of lakes which today no longer exist OutwashCreated by sediment washed out of melting glaciers

HOW LANDFORMS CHANGE (p. 10) Coal deposits are believed to have formed when tropical forests fell into swamps, decomposed, and were buried and then compressed into rock. Geologists have discovered coal deposits in Antarctica. How is this possible?

Alfred Wegener ( ), a German meteorologist, suggested that Earth’s continents were once joined in a single land mass called Pangaea. – 200 million years ago, Pangaea broke into two sections: Laurasia and Gondawanland. These continents continued to divide and remain in this process today. This process is referred to as continental drift. – His theory was based on the shape of the continents and evidence from fossil and rock formations. – Wegener thought volcanic activity caused these changes, but could not prove it. For this reason his theory was discounted as incomplete.

Continental Drift

Wegener based his theory on the shape of the continents and evidence from fossil and rock formations.

J. Tuzo Wilson ( ), a Canadian geologist, brought life back to Wegener’s theory, when he noted that volcanic activity took place at mid-ocean ridges. – Wilson noted that rock layers on either side of the ridges were remarkably similar (matching age and magnetic imprints). – He theorized that volcanic activity caused new ridges to split the ocean floor and push continents apart. This process is referred to as sea-floor spreading and has been verified in recent decades by satellite photography, measurement of seismic activity, and the study of rocks and fossils.

Patterns of plate movement (p. 11) The pieces of crust that spread apart are called plates and the movement of places is known as plate tectonics. Plates rest on top of the asthenosphere (semi-liquid magma). – This molten rock is hotter and lighter when closer to the earth’s core and will rise. – When molten rock rises towards the crust, it cools and becomes dense (heavier) and will begin to sink. – This movement of magma creates a circular pattern below the crust. When molten rock moves below the crust, plates move with it, as if floating.

When plates move towards each other, squeezing together, they create a compressional force. This causes rock layers to bend, warp, or be pushed upwards. Compressional forces occur at places called subduction zones. A heavier (oceanic) plate slips under or is pressed beneath a continental plate. When plates move away from (or past) each other, breaking apart, they create a tensional force. This causes rock layers to sink or drop. Tensional forces occur at ridge zones. As plates separate through volcanic activity, lava cools and hardens creating elevated ridges on the plates’ edges.

*Complete “Plate Tectonics Lab” activity*

Mountain Building (p. 13) Most mountain ranges are found on the margins (edges) of continents. Continental plates lie against oceanic plates and are compressed, causing rock layers to be squeezed upward. This produces mountains. Mountains are can be formed in one of the following ways: folding, faulting, or volcanic activity.

Folding Rocks are bent, buckled and pushed upward in a folding pattern as a result of compressional forces. Rock layers take the form of a wave pattern. The upfold (upper part or crest) of the wave is called an anticline, while the downfold (lower part or trough) is called a syncline.

Faulting Rocks fracture or break through either compressional or tensional forces: – Compressional forces push rocks together and cause fracturing. – Tensional forces separate rocks and cause fracturing. When faulting occurs, rock position often readjusts, causing some sections to move upwards, while others drop. Fault FormationCharacteristics Normal FaultRock on one side of a break drops down lower than the other. (tension) Rift Valley (graben)Two normal faults occur and the rock between them drops. (tension) Block Mountain (horst) Two normal faults occur and the rock between them is pushed up. (tension) Reverse FaultA fault occurs and one section of rock is pushed over the other. (compression) Overthrust FaultSame as a reverse fault, except rock layers had already been folded at some point in the past. (compression)

A normal fault in Trinidad. Note the darker rock layers on the left that have dropped from their original location. An overthrust fault in Devon, UK, identifiable through the folded rock layers above the fault. A reverse fault. The section of rock on the right has been broken and pushed over the section on the left.

Volcanic Activity Plates push against each other and create intense heat and pressure. This intense heat melts the rock beneath the crust, changing it magma. Magma flows into cracks and fractures in rock. This is referred to as intrusive activity. If magma reaches the surface, extrusive activity occurs. When magma reaches the surface, it is called lava. Small molten rock fragments and gas is called ash, or cinders. Volcanoes that we see are caused by Extrusive volcanic activity. A single opening in a volcano, through which lava pours, is called a vent.

Volcanic eruptions may be either mild or explosive: Mild eruptions occur when lava flow is thin and flows easily. There is less build up of pressure from lava and gases to plug or block the vent. Lava tends to pour out. Explosive eruptions occur when lava flow is thick and slow. Pressure builds are thick lava and large amounts of gases, ash and cinders begin to block the vent.

Types of volcanoes Describe the differences you see in the visuals.

Type of VolcanoCharacteristics Ash-and-Cinder Cone (a) Formed from explosive eruptions Thick, slow flowing lava that solidifies quickly Symmetrical in shape (looks the same on all sides) Steep sides A great amount of ash and cinders Large crater Shield Cone (c) Formed from mild eruptions Very thin liquid lava Broad base Little to no ash and cinders Nearly flat cone Composite Cone (b) Alternating violent eruptions and quiet periods Layers of ash and cinders intermixed with layers of solidified lava Inconsistency in composition results of weak points along the sides. Lava flows through these weak points creating small lateral vents. *Complete “Mount Pinatubo” Case Study*

*Complete questions 21 (c, d) and 22, on p. 20.*