Physical Geography Landforms Overview Geologic Time Movements of

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 (1600 s) • No mechanism for motion

• 1915 Alfred Wegener proposes theory of continental drift. • Supercontinent Pangaea (‘all-earth’) [225 mya]. • 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 (1930 s) – thermal convective cells in the upper mantle (aesthenosphere) – theory is largely ignored

History of Plate Tectonics • In the 1960 s, 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 – intrusive: formed inside 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 (Ca. CO 3) Sandstone (larger grains) Shale (fine grains)

Where do Sedimentary Rocks Form? Marine Terrestrial environments (non environments · Continental shelf -marine) · Rivers and floodplains (fluvial environment) · Lakes · Deserts (aeolian environment) · 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?

Metamorphic Amitsoq What type? 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

Morro Rock, CA What type?

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

The Rock Cycle