Chapter 14- The internal Processes Flashcards
Alfed Wegner
was a German meteorologist and geophysicist.
Who was Alfred Wegener; what was his evidence for continental drift?
He found that the continental margins of Africa and South America fit together with jigsaw-puzzle-like precision. Also, he determined that the petrologic (rock) records on both sides of the Atlantic show many distributions- such as ancient coal deposits- that would be continuous if the ocean did not separate them. Moreover, when models of the continents are moved back into the Pangaean (Pangaea: Greek word for “whole land”) configuration, mountain belts in Scandinavia and the British Isles match up with the Appalachian Mountains in eastern North America.
Why was his theory rejected? Alfred Wegener
Because, most scientists felt that two difficulties made the theory improbable if not impossible. 1. Earth’s crust was believed to be too rigid to permit such large-scale motions- after all, how could solid rock plow through solid rock? 2. Wegener did not offer a suitable mechanism that could displace such large masses for a long journey.
Evidence for the current scientific theory of Plate Tectonics
Midocean ridges, Paleomagnetism, and Seafloor spreading
Midocean ridges
40,000-mile interconnected chain under the ocean
Paleomagnetism
Earth’s magnetic field reversals in geologic history
Seafloor spreading
younger crust near ridges, older crust as you move away toward continents
Plate Boundaries – understand the differences and the potential for hazards/disasters among these:
Divergent Boundaries
- Mid-ocean Ridges (e.g., Mid-Atlantic Ridge, East Pacific Rise)
- Continental Rift Valleys (e.g., African Great Lakes, Death Valley in California)
- Convergent Boundaries
- Ocean Plate-Continental Plate (e.g., Andes Mountains, Cascade Mountains)
- Ocean Plate-Ocean Plate (e.g., island arcs, Japan, Aleutian Islands)
- Continental Plate-Continental Plate (e.g., Himalayas)
- Transform Boundaries (lateral slip): when two plates slide past each other, horizontally.
- Plates “snag” until a sudden slip releases energy and causes EQs (e.g., San Andreas Fault).
Where is the Pacific Ring of Fire and what is its significance in creating landforms?
The Ring of Fire isn’t quite a circular ring. It is shaped more like a 40,000-kilometer (25,000-mile) horseshoe. A string of 452 volcanoes stretches from the southern tip of South America, up along the coast of North America, across the Bering Strait, down through Japan, and into New Zealand.
The Ring of Fire is a direct result of plate tectonics: specifically the movement, collision and destruction of lithospheric plates (e.g. the Pacific Plate) under and around the Pacific Ocean. The collisions have created a nearly continuous series of subduction zones, where volcanoes are created, and earthquakes occur. -GOOGLE
Hot Spots appear at the crust above mantle plumes. Where are they? What can happen here?
A hot spot is an area on Earth over a mantle plume or an area under the rocky outer layer of Earth, called the crust, where magma is hotter than surrounding magma. The magma plume causes melting and thinning of the rocky crust and widespread volcanic activity. -GOOGLE
Volcanism - Where are volcanoes distributed on Earth’s surface, and why at those places?
Volcanoes are not randomly distributed over the Earth’s surface. Most are concentrated on the edges of continents, along island chains, or beneath the sea forming long mountain ranges. -GOOGLE
Volcanic Activity depends on magma chemistry, and volcanoes are classed by styles of eruption:
The most common felsic rock is granite, typical of Earth’s crust
- Magma heavy in silica will tend to clog volcanic neck, produce violent eruptions
- Mafic magmas - rich in magnesium and iron
- Common mafic rocks include gabbro and basalt, typical of the ocean crust
- Mafic magmas are less viscous, flow more evenly, less explosiveness
Examples of common Volcanic Hazards? Volcanic Peaks – know differences between these features:
Shield volcanoes= Shield volcanoes consist largely of thin lava flows, with minor pyroclastic (mainly ash) layers.,
- Composite volcanoes= A composite volcano is a symmetrical cone with steep sides that are built of alternating layers of lava, ash, pumice, blocks, and tephra.,
- Lava domes= a circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano.,
- Cinder cones= simple volcanoes which have a bowl-shaped crater at the summit and steep sides. They only grow to about a thousand feet, the size of a hill. They usually are created of eruptions from a single opening, unlike a strato-volcano or shield volcano which can erupt from many different openings.,
- Calderas= a large depression formed when a volcano erupts and collapses. During a volcanic eruption, magma present in the magma chamber underneath the volcano is expelled, often forcefully. When the magma chamber empties, the support that the magma had provided inside the chamber disappears..
Plutons
large bodies of igneous magma that cool/harden underground, revealed later by erosion.
intrusive igneous features
e.g., Batholiths, Volcanic Necks, Laccoliths, Sills, Dikes
