Chapter 13: Introduction to Landform Study

The Structure of Earth Understanding of Earth’s structure based on minute fraction of total depth (<8 miles) Good deal of understanding inferred by geophysical means 4 regions of Earth’s interior Figure 13-1

The Structure of Earth Crust Thinnest layer Base Depth of 5 km below ocean to near 20 km below land < 1% of Earth’s volume, 0.4% of Earth’s mass Base Moho discontinuity Composed of mostly silicate material Part of lithosphere Ocean crust (basalt) vs. Continental crust (granite)

The Structure of Earth Mantle Largest and thickest layer Makes up 84% of total volume, 67% of total mass Extends to depth of 2900 km (1800 miles) Magnesium with material from both crust & core 3 sublayers Lithosphere (upper mantle) Cool/brittle rock Asthenosphere Plastic quality of rocks Lower mantle Rigid/brittle rock

The Structure of Earth Core Composition: Iron & Nickel Outer core Outer/inner core combined = 15% of Earth’s volume & 32% of Earth’s mass Outer core Molten (liquid), extends to depth of 5000 km Generates Earth’s magnetic field Magnetic poles not the same as the axial poles Inner core Solid, dense mass Rotates independently

The Structure of Earth “Continental drift” Plate tectonics—large lithospheric plates slide along the top of the asthenosphere

The Composition of Earth Minerals—naturally formed compounds & elements of Earth Characteristics Solid Found in nature Inorganic Specific chemical composition Specific crystal structure Atoms arrange in patterns to form crystals

The Composition of Earth Figures 13-2 & 13-3 The Composition of Earth Important crustal minerals Silicates—oxygen + silicon Most common elements in the lithosphere Oxides—oxygen + another element Sulfides—sulfur + another element Sulfates—sulfur + oxygen Carbonates—light-colored minerals composed of carbon, oxygen + another element (i.e., limestone) Halides—derived from word “salt”, salty minerals Native elements—gold and silver Also appear as elements

The Composition of Earth Earth’s composition as a whole Primarily iron & oxygen. Silicon is abundant in the crust Iron & Magnesium are more abundant in the lower mantle & core due to density

The Composition of Earth Composition of Earth’s crust is significantly different from Earth as a whole.

The Composition of Earth Rocks—composed of 2 or more minerals Fewer than 20 minerals make up 95% of the composition of crustal rocks Bedrock Solid rock; no weathering Outcrop Bedrock exposure Regolith Partially weathered rock Petrology— characteristics of different rocks Figure 13-4

The Composition of Earth Igneous rocks Igneous—“fiery inception” Crystallized magma/lava Magma—molten rock beneath Earth’s surface Lava—molten rock on Earth’s surface Pyroclastics

The Composition of Earth Igneous Rock Classification 2 Compositions Light colored (felsic) Dark colored (mafic) 2 Textures Plutonic (intrusive) Rocks cool slowly beneath Earth’s surface Coarse-grained Volcanic (extrusive) Rocks cool rapidly on Earth’s surface Fine-grained

The Composition of Earth \ Figure 13-6

Silica Content of Magma The Composition of Earth Silica Content of Magma Basalt 45-50% SiO2 Andesite 60% SiO2 Rhyolite 70-75% SiO2

The Composition of Earth Sedimentary Rocks Sediments Lithification Putting fragments back together Compaction Cementation Iron oxide, silica & calcium carbonate Deposited in layers Clastic Rocks Pieces of other rock Chemical Rocks Precipitated materials Organic Rocks Plant or animal parts Figures 13-9 & 13-13

The Composition of Earth Metamorphic Rocks Re-crystallizing pre-existing rock Heat and pressure Foliation Banded, layered, or wavy characteristic after extreme pressure Types Contact metamorphism Regional metamorphism Burial metamorphism Shock metamorphism Pyro-metamorphism Figure 13-16b

Quartzite comes from sandstone Slate comes from of shale

The Composition of Earth Metamorphic Rocks hornblende stress stress Granite (igneous) Gneiss (metamorphic)

The Composition of Earth Rock cycle—processes where rocks transition from igneous rocks to sedimentary rocks to metamorphic rocks Not a linear path Figure 13-17

The Composition of Earth Continental rocks Sedimentary rocks = 75% of continents Continental crust: sial Granite Ocean floor rocks Ocean floor crust: sima Basalt More dense than continental rocks = subduction Figures 13-18 & 13-19

The Composition of Earth Isostasy: equilibrium between gravity & buoyancy Weight of rocks / glaciers / sediments on continental shelf Adjustment in the density of the asthenosphere Earth’s Surface Figure 13-20

The Study of Landforms Topography vs. Landform Elements of landform study Structure Geology Process Actions creating landforms Slope Drainage Relief Change in elevation in an area Fundamental questions of geographic inquiry: What, where, why, and so what? Figure 13-22

The Study of Landforms Topography – Nebraska

The Study of Landforms Topography – Wyoming

Some Critical Concepts Internal and External Geomorphic Processes Internal: inside Earth, increase relief External: outside Earth; decrease relief Figure 13-23

Some Critical Concepts Uniformitarianism “The present is the key to the past” Processes which shaped the landscape of the past are the same that will shape the future Geologic time Vast periods of time over which geologic processes operate Geologic time in 1 year Figure 13-24

Scale and Pattern The Pursuit of Pattern—major landform assemblages of the world Figure 13-26

Summary Earth’s structure is presumed based on geophysical research Earth’s interior consists of four regions Earth’s composition consists of elements or compounds of elements called minerals Seven primary types of minerals exist Rocks are composed of minerals Igneous rocks are those formed by cooling and solidification of molten rock Plutonic rocks are those which form within the Earth Volcanic rocks form on the Earth’s surface Sedimentary rocks form as a result of transport of mineral material by water Two primary types of sedimentary rocks, clastic and chemical/organic sedimentary rocks Metamorphic rocks are igneous or sedimentary rocks that have been drastically changed by heat and/or pressure The rock cycle is the transition cycle through the different rock types Continental and ocean floor rocks possess different characteristics which are important in geophysical processes Isostasy is the recognition of the differences between continental crust, oceanic crust, and mantle Landforms are characterized by structure, process, slope, and drainage Internal and external geomorphic processes are responsible for the relief of Earth Uniformitarianism allows us to use geologic time to infer what happened in the past based on the present