Created by: Genny, Danish, Aalap

Concept that all continents were once joined in a landmass: Pangaea Eventually they broke apart and drifted away, gradually forming the world we have today Cause: movement of tectonic plates

Types of Plates: Oceanic and Continental

Convergent Divergent Transform

Convection currents generated by the uneven heating of magma in the Earth’s interior are what cause Earth’s crust to break apart and move.

Where: convergent plate boundaries What: two plates collide, and the heavier plate sinks underneath the less dense plate and is subducted back into the Earth’s mantle Why: the difference in density

Examples of Subduction: Oceanic and Continental plates collide, and the oceanic crust subducts beneath the continental crust due to difference in density. Andes Mountains

Where: Convergent plate boundaries, usually oceanic and continental plates What: As oceanic plate subducts underneath continental plate, the sediment that breaks off attaches to the continental plate. Result: expansion of continental plates, along with pieces of oceanic crust preserved on land called “ophiolites”

Example: Elder Creek Ophiolite located in the Coast Range ophiolites off the coast of California Example: Peru/Chile border: Nazca Plate subducts underneath the South American Plate

Opposite of Accretion What: the descending plate along with parts of the overriding plate subducts underneath Result: Decrease in sizes of continents

Spreading occurs at divergent boundaries (Plates moving apart) Sea-floor spreading is when there is a divergent boundary in the middle of the ocean floor Divergent boundaries on continental crust causes rift valleys to form on land

Occurs between two oceanic plates As the plates move apart, magma rise through the rift and hardens to form new crust Ocean floor gradually extends and size of plates increase The age of the rock increases as you are moving away from the rock As magma piles up along cracks, a long chain of mountains form. These are called oceanic ridges. (Ex. Mid-Atlantic Ridge)

Age of crust (youngest = red)

As lava cools it becomes magnetized in direction of Earth’s magnetic field Scientists learned that Earth’s magnetic field has reversed polarity many times Helps provide history of the rate of sea- floor spreading (Fast=broad, Slow=squeezed)

Rift valleys are formed at divergent plate boundaries on land At the early stage of development, rivers flow into the valley. As the valley becomes deeper, more water flows in and eventually causes an ocean basin

East African Rift Valley Eventually Africa will split into 2 sub-continents East African Rift Valley Red Sea

Plate movements cause stress, which leads to deformation Three types of deformation: Shearing (Opposite) Tension (Thinner) Compression (Squeeze) 3 types of folds: Anticlines (Arch), Synclines (Down), and Monocline (Dip)

Anticline Syncline Monocline

Caused by shearing. This motion results in transform boundary San Andres Fault in California

Cause by tension forces. Hanging wall (top) Footwall (bottom). Results in divergent boundaries

Cause by compression. Same as normal fault except walls are opposite

Forces that “build” landforms. Examples: mountains, islands, volcanoes, etc. Forces that “break down” landforms. Examples: weathering, erosion, subduction, faults, etc.

These forces form the landmasses we have today, affecting spatial patterns around the globe. It influences people’s everyday decisions as to where they live and how they interact with the environment.