Physical Geography:
Landforms

Overview
• Geologic Time
• Movements of the Continents
• Earth Materials
• Tectonic Forces
• Weathering and Erosion Processes
• Erosional Agents and Deposition

Geologic Time
Pretend the age of the earth (4.6+ billion years) is compressed into one calendar year.
January 1 - Earth and planets formed
Early March - liquid water stands in pools.
Late March - earliest life
July - oxygen is important part of atmosphere
October 25 – multi-cellular organisms
Late November - plants and animals abundant
December 15 to 25 - dinosaurs arise and disappear
11:20 pm, December 31 - Humans appear
One second before midnight - Automobile invented

What is ‘tectonics’?
• From Greek ‘tektonikus’ meaning building or construction
• Plate tectonics refers to the process of earth crust formation, movement, and destruction.

What is a ‘Plate?’
• Lithospheric plate: crust + upper mantle
• Aesthenosphere: plastic mantle

History of Plate Tectonics
• ‘Fit’ of coastlines recognized early
– Sir Francis Bacon (1600s)
• No mechanism for motion

• 1915 Alfred Wegener proposes theory of continental drift.
• Supercontinent Pangaea (‘all-earth’) [225mya].
• Fragmentation and drift to current positions.

Plate
Movement
History

• Wegner’s evidence
– Fit of continents
– Fossil plants, animals, rock types / geology
• match on opposite shores
• deposits inconsistent with current geography

Striking Match of Geologic
Regions

Striking Match of Biological Regions

History of Plate Tectonics
• Problem with continental drift?
– No sound mechanism for the ‘drift’!
– Wegner hypothesizes spin of earth or tides…..

History of Plate Tectonics
• New theory for motion: Arthur Holmes
(1930s)
– thermal convective cells in the upper mantle
(aesthenosphere)
– theory is largely ignored

History of Plate Tectonics
• In the 1960s, Harry Hess and Robert Deitz
(geophysicists) propose sea floor spreading along mid-oceanic ridges for plate motion.

Sea Floor Spreading

Plate Tectonics Theory
• Continental Drift + Sea Floor Spreading
+ new data  Theory of Plate Tectonics

Plate Tectonics Theory
• Plate boundaries: main location for
Earth’s volcanic and earthquake activity.
This is main place where mountains are created.
• Type of plate boundary determines activity.
• 3 types
– diverging (spreading)
– converging (colliding)
– transform (sliding past each other)

Geography of the Plates
• 7 major plates; several minor plates
• Small plates / boundaries still unknown

Plate Margins: how do we know?
• Marked by volcanic and tectonic activity

Convergent Plate Boundaries
• Activity:
– subduction; shallow to deep earthquakes; volcanism (continental)
• Features :
– ocean trench; explosive volcanic mtns on continental margin

Divergent Plate Boundaries
• Landscape features:
– land: rift valleys, volcanic mountains, thinning crust
– ocean/sea: rift valleys, mountain ranges

Divergent Plate Boundaries
• Examples:
– Atlantic Mid-Oceanic
Ridge
– Red Sea
– Rift valleys of eastern
Africa

The Rock Cycle

Earth Materials
• Formation of Earth
• Three major rock types
– Igneous
– Sedimentary
– Metamorphic

Formation of the Earth’s Interior
• @5 bya, plantesimals (meterorites,icy comets) collide  heat released
(Kinetic energy to thermal energy)
• Entire planet melts (still cooling today)
• Gravity sorts materials by density
– Fe in center
– Si and O compounds towards surface

The Earth’s Interior
• General trends: temperature, density
• Horizon composition, behavior
Distance: 6730 km (3963 miles)

Igneous Rocks
• Igneous (ignus = fire)
• Formed from the cooling of molten rock
(magma/lava), a process called crystallization.
– Slow cooling  larger crystals > dense rock
– Rapid cooling  small crystals > lighter rock

• Two classes of igneous rocks
– in trusive: formed in side the Earth
– extrusive: formed at Earth’s surface

Igneous
Extrusive
Landscapes
Volcanic Crater and Cinder Cone: Indonesia
Volcanic cones, obsidian flow: Mono
Craters, CA
Volcanic neck and dike: Shiprock, NM

Igneous Extrusive Rocks
• Cools rapidly - exposed to surface
• No visible crystals
• Examples
- rhyolite - andesite -basalt

Some unique volcanic rock types
 Pumice
(vesicular)
- sometimes so light it floats!
Obsidian 
– glassy, ‘curved’ fracturing
– used for arrowheads by
Native Americans

Igneous Intrusive Rocks
• Cools slowly (thousands of years)
• Visible crystals
• Examples
- granite

Typical Igneous Intrusions

Exposed Batholiths
Sierra Nevada, CA

Sedimentary Rocks

Sedimentary
Rocks
Relative Abundance by
Type
Compaction
Cementing
Formation

Limestone (CaCO
3
)
Sandstone (larger grains)
Shale (fine grains)

Where do Sedimentary Rocks
Form?
Terrestrial environments
(non-marine)
 Rivers and floodplains
(fluvial environment)
 Lakes
 Deserts (aeolian environment)
Marine environments
 Continental shelf
 Continental slope and rise (deep sea fans)
 Abyssal plain
 Beach and barrier islands

Metamorphic Rocks or That’s very Gneiss, but
I don’t give a Schist!
Schist (narrow foliation)
Gneiss (broad foliation)

Which Type?

Which Type?
Sedimentary - limestone and shale

What type?

What type?
Metamorphic -
Amitsoq
Gneiss, Greenland, 3.8 billion old

What type?

What type?
Sedimentary -
Sandstone in
Utah

What type?

What type?
Extrusive Igneous -
Reunion Island, Indian Ocean

What type?

What type?
Folded Sedimentary -
‘Sheep Fold’, Wyoming

What type?

What type?
Sedimentary -
Vasquez
Rocks, Southern California

What type?
Morro Rock, CA

Morro Rock, CA
Devil’s Tower, Wyoming
What type?
Intrusive Igneous

The Rock Cycle