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Physical Geography: Landforms. Overview Geologic Time Movements of the Continents Earth Materials Tectonic Forces Weathering and Erosion Processes Erosional.

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Presentation on theme: "Physical Geography: Landforms. Overview Geologic Time Movements of the Continents Earth Materials Tectonic Forces Weathering and Erosion Processes Erosional."— Presentation transcript:

1 Physical Geography: Landforms

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

3 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

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

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

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

7 1915 Alfred Wegener proposes theory of continental drift. Supercontinent Pangaea (‘all-earth’) [225mya]. Fragmentation and drift to current positions.

8 Plate Movement History

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

10 Striking Match of Geologic Regions

11 Striking Match of Biological Regions

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

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

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

15 Sea Floor Spreading

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

17 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)


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

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

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

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

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

24 The Rock Cycle

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

26 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

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

28 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

29 Two classes of igneous rocks –intrusive: formed inside the Earth –extrusive: formed at Earth’s surface

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

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

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

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

34 Typical Igneous Intrusions

35 Exposed Batholiths Sierra Nevada, CA

36 Sedimentary Rocks

37 Compaction Cementing Sedimentary Rocks Formation Relative Abundance by Type

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

39 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


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

42 Which Type?

43 Sedimentary - limestone and shale

44 What type?

45 Metamorphic - Amitsoq Gneiss, Greenland, 3.8 billion old

46 What type?

47 Sedimentary - Sandstone in Utah

48 What type?

49 Extrusive Igneous - Reunion Island, Indian Ocean

50 What type?

51 Folded Sedimentary - ‘Sheep Fold’, Wyoming

52 What type?

53 Sedimentary - Vasquez Rocks, Southern California

54 What type? Morro Rock, CA

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

56 The Rock Cycle

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