Physical Geography: Darrell Hess: Chapter 14 Part A

Chapter 14: The Internal Process Part A

Chapter 14: The Internal Process Part A

Ashley Adams

Donald Agaba

Alysha Baldwin

Cory Bragg

Ashley Adams

Donald Agaba

Alysha Baldwin

Cory Bragg

The Impact of Internal Processes on Landscape

What are Internal Processes?• Geological forces that shape the physical appearance of the

world. • such as earthquakes, erosion, resource depletion, and plate

movements.• Physical Activity exists at the surface level. • examples of these processes on our landscape include the

creation of the Grand Canyon, separating Pangaea into the multiple continents we have now, and effecting the tides.

Rigid Earth To Plate Tectonics

• Until the 20th century, most scientists believed the Earth's crust was rigid.

• Thought the continents were fixed in place; immobile.

• Thought that continents were formed as a result of magma cooling in irregular shapes.

Wegener’s Continental Drift

Alfred Wegener:• Revived the idea of continental drift, first introduced by

early scientists.• Collected a lot of evidence to support Pangaea theory.• Pangaea means "whole land" in Greek.

Alfred Wegener Continued

• He noted the many similarities between the continents:– Eastern South America and West Africa fit right into each other.– Similar mineral deposits on either continent.– N. American and Scandinavian mountain ranges match up.– Fossils from the same species were found on different continents.– Similar fauna and flora still found in places thousands of miles apart-

• South Africa, Australia and Madagascar.

Wegener Continued

• Many scientists discredited his theories.

• His theories didn't add up to experts back then because plate tectonics had not yet been discovered.

Plate TectonicsSeafloor Spreading

Convection currents bring magma from the asthenosphere up through fissures in the oceanic lithosphere at the mid-ocean ridge. The cooled and solidified magma become a new portion of the of the ridge along the ocean floor, and the two sides of the new portion then spread away from each other. In places where denser ocean lithosphere converges with less dense continental lithosphere, the ocean lithosphere slides under the continental. This process is called Subduction. Magma produced by subduction rises to form volcanoes and other igneous intrusions.

Seafloor Spreading Continued

Verification of Seafloor Spreading:

Paleomagnetism: past magnetic orientation.- When any rock containing iron is formed, like the ocean floor, it is magnetized so that the

iron-rich grains become aligned with Earth’s magnetic field. The orientation then becomes a permanent record of the polarity of Earth’s magnetic field at the time the rock solidified.

- New basaltic ocean floor is magnetized according to the existing magnetic field of the Earth. As the ocean floor spreads away from a ridge, a symmetrical pattern of normal and reversed magnetic polarity develops on both sides of the spreading center.

Seafloor Spreading Continued

Ocean Floor Cores: Final confirmation of seafloor spreading was obtained from core holes drilled into the ocean floor by a research ship. Several thousand ocean floor cores of sea bottom sediments were analyzed, and it was evident that sediment thickness and age increase with increasing distance from the mid ocean ridges. This indicates that sediments farthest from the ridges are the oldest. At the ridges, ocean floor material is almost all igneous, with little accumulation of sediment. Any sediment near the ridges are thin and young.

Plate Boundaries

Divergent:

Usually represented by a midocean ridge. At this type of boundary, magma from the asthenosphere wells up in the opening between plates. This upward flow of molten material produces a line of volcanic vents that spill out basaltic lava onto the ocean floor. They are said to be called “constructive” because material is being added to the crustal surface.

Divergent boundaries can also develop within a continent, resulting in a continental rift valley, such as the East African Rift Valley stretching from Ethiopia to Mozambique.

Plate Boundaries Continued

Convergent BoundariesAt a convergent boundary, plates collide and are sometimes “destructive” boundaries because they result in removal or compression of the surface crust. Convergent boundaries are responsible for some of the most massive and spectacular of earthly landforms: major mountain ranges, volcanoes, and oceanic trenches. There are 3 major types: oceanic-continental, oceanic-oceanic, and continental-continental.

Plate Boundaries Continued

Oceanic-Continental Convergence

Because oceanic lithosphere includes dense basaltic crust, it is denser than continental lithosphere, oceanic always underrides continental when the two collide. The dense oceanic plate sinks to the asthenosphere, which is subduction. Wherever this boundary occurs, mountain ranges are formed, and a parallel oceanic trench develops as the ocean floor is pulled down by the subducting plate.

Oceanic-Oceanic Convergence

If the convergent boundary is between two oceanic plates, subduction takes place. As one of the oceanic plates subducts under the other, an oceanic trench is formed, shallow and deep focus earthquakes occur, and volcanic activity is initiated with volcanoes forming on the ocean floor. With time, a volcanic island arc occurs.

Continental-Continental Convergence

Where there is a convergent boundary between two continental plates, no subduction takes place because continental crust is too buoyant to subduct. Instead, huge mountain ranges, such as the Alps and Himalayas are built up.

Plate Boundaries Continued

Transform Boundaries:

At a transform boundary, two plates slip past one another laterally. This boundary is classified as conservative because the plate movements are basically parallel to the boundary, a situation that neither creates new crust or destroys old. Transform faults are associated with a great deal of seismic activity, commonly producing shallow-focus earthquakes.

Volcanism

Refers to all the occurrences connected with the origin and the movement of molten rock

This includes explosive volcanic eruptions and the solidification of molten material below the surface

• Magma- Molten material below the surface

• Lava- Magma extruding onto Earth’s surface, where it will cool and harden

The ejection of lava into the open air can be explosive, destroying the area around it

Items such as rock fragments, lava blobs, ashes, and dust can be hurled up with the lava in large quantities

• Pyroclastic- Solid rock fragment thrown into the air by volcanic explosions

Volcano Facts

• A volcano is considered active if it has erupted at least once within historical times or is likely to do so again

• There are 550 active volcanoes in the world– 15 of them will erupt this week– 55 this year– 160 this decade

• 1-2 volcano eruptions will erupt with no historic activity

• Magma rises from the interior by-– Eruption from active volcanoes– By flooding out of fissures

• Some volcanoes have an active life for only a few years, whereas other volcanoes are randomly active for thousands of years

Pacific Ring of Fire

The most notable area of volcanism in the world

75% of the world’s volcanoes

The most volcanic places on earth are also the most fertile

Magma Chemistry and Styles of Eruptions

Volcanic Activity

• Volcanoes provide vital services to the planet– Much of the eater on Earth today was due to the water vapor during volcanic

eruptions during early history of our history

• Magma contains:– Phosphorus– Potassium– Calcium– Magnesium– Sulfur

• All of the elements in magma are needed for plant growth

• When lava hardens it releases the nutrient into the soil which could take decades of centuries– When ash is blasted out the nutrients can go into the soil

Lava Flows

• A lava flow spreads outward parallel with the surface it’s flowing over

• The speed and distance covered by a lava flow depends on its thickness– The thickness depends on the silica content

• Low-Silica Basaltic Lava-– Associated with shield volcanoes– More fluid and fast moving (15 mph)– Can travel up to 75 miles before hardening– Paths of lava are predictable and injuries can be avoided

• High-Silica Lava-– Associated with composite volcanoes around the rim of the Pacific– Much thicker than basaltic lava– Move short distances down the slopes of the volcano

Flood Basalt

Flood Basalt- A large scale outpouring of basaltic lava that may cover an extensive area of Earth’s surface

Scientists think that the dinosaur’s extinction was a result of the flood basalt eruptions of the Deccan Traps

Types of Volcanoes Peaks

1. Shield Volcanoes

• Have gentle slopes– Even if volcano is massive and high it will not have a steep slope

• Consist of layer after layer of solidified lava flows

2. Composite Volcanoes (Stratovolcano)

• Emit higher silica “intermediate lavas” – Andesite

• Explosively erupt

• Are steep-sided in the shape of a cone

Mt. Fuji, Japan

3. Lava Dome (Plug Dome)

• Are small with an irregular shape

• Have thick lava– High-silica rhyolite is too thick and pasty to flow very far

• May develop within craters of composite volcanoes when the thick lava moves up the vent

Lassen Peak, California

4. Cinder Cone

• The smallest of the volcano peaks that has steep-sides

• Their cone-shaped peaks are built from the pyroclastic materials that were ejected from the volcano vent

Paricutin, Mexico

Calderas

Calderas- A large, steep-sided, roughly circular depression

• Calderas are formed when a volcano explodes, collapses, or both

• The diameter is many times larger than the original volcanic vent(s)

• Shield volcanoes can develop summit calderas– The magma chamber below the summit can empty and collapse– Thus the creation of a shallow caldera

Crater Lake, Oregon

Mount Mazama (Crater Lake)

Volcanic Necks

Volcanic Neck- a small, sharp spire that rises abruptly above the surrounding land

Volcanic necks represent the throat of an old volcano that filled with solidified lava after its final eruption

Volcanic Hazards

• There are more than 50 volcanoes that have erupted within the last 200 years in the United States– Washington– Oregon– California– Alaska– Hawai’i – Yellowstone National Park

• Future eruptions could expose large

numbers of people to a wide range

of volcanic hazards

Monitoring Volcanic Hazards

• The U.S. Geological Survey and research universities are now looking back at previous eruptions to map out the most likely paths of pyroclastic flows and mudflows from volcanoes

• The monitoring includes:– Measuring slight changes in the slope of a mountain using sensitive

“tiltmeters” • Tiltmeters detect swellings of a volcano with magma

– Measuring variations in gas composition and quantity vented from a volcano that may indicate changes in magma

– Monitoring earthquake activity below a volcano

• Knowing this can help authority figures to know where to evacuate local populations when the next volcano erupts

Volcanic Gases

• Large amounts of gases are releases during an eruption– Mostly water vapor– Carbon dioxide– Sulfur dioxide– Hydrogen sulfide– Fluoride

• Sulfur dioxide can mix with water and come down to land as sulfuric acid– This can harm vegetation– Can reflect incoming solar radiation which can alter global weathering

Eruption Column and Clouds

• The ejection of pyroclastic material and gases from a volcano can form an eruption column– Can reach altitudes of 10 miles of more

• Large fragments of solid rick drop to the ground immediately around the volcano (also called volcanic bombs)

• Smaller fragments of volcanic ash and dust form an eruption cloud where large amounts of ash may fall– This can damage crops or even cause the collapsing of buildings

Pyroclastic Flows

• Result from the collapse of a lava dome or from the rapid subsidence of an eruption column during an explosive eruption of a volcano

• Can travel down a volcano at or faster than 100 mph– Burns, and buries everything in it’s path

Volcanic Eruptions

← Lateral Blast

Volcanic Mudflows

Volcanic Mudflows- A fast-moving, muddy flow of volcanic ash and rock fragments

• Can be caused by a loose mantle of ash and pyroclastic flow deposits on the slopes of a volcano– Mobilized by heavy rains or melting ice/snow

• Water mixes with the pyroclastic material which produces a fast-moving slurry of mud and boulders

• They can reach a speed up to 30 mph

• They can travel up to 50 miles

Igneous Intrusion

Igneous Intrusion- Features formed by the emplacement and cooling of magma below the surface.

Types of Igneous Intrusion and their features:• Batholiths: Largest and most amorphous.• Usually at least 100km of surface area.• Unknown depth• Form the core of many mountain ranges

– Example:Sierra Nevadas, Front Range in Colorado, and Idaho's Sawtooth.

• Core is usually made of granite. Granite is eventually exposed with time due to erosion.

Laccoliths

Laccoliths• Produced when slow flowing magma gets trapped between horizontal

rock.• Resists magma flow and becomes mushroom shaped - forms hills.

Sills

• Long, thin, intrusive body.

• Shape determined by the structure of pre-existing rocks.

Dikes

• Vertical sheets of magma.

• Force their way through fractures in pre-existing rocks.

• Usually narrow.

• Can stretch for many miles.

Veins

• Least visible.

• Large numbers of veins found on ocean floor.

• Formed when magma is forced through small fractures in rocks.