GEOL 101 Chapter 13

Seamounts

(Submarine volcanoes) 1. Over a million seamounts exist 2. Found in all ocean floors but most common in the Pacific 3. Many form near oceanic ridges or over a hot spot

Rift Valley

(a deep, down-faulted structure) exists on the axis of most ridges

What are the 4 main features of a deep ocean basin?

1. deep-ocean trenches 2. abyssal plains 3. seamounts and guyots 4. oceantic plateaus

Continental margins

Outer margins of the continents and the transition to oceanic crust

Oceanic Plautaes

Vast outpourings of basaltic lavas on the ocean floor (Resemble continental flood basalts)

A seamount may grow large enough to emerge as a _________ _________.

Volcanic Island

Oceanic ridges

A broad, linear swell at a divergent plate boundary

Modern bathymretric techniques

After World War II the US Navy developed sidescan sonar Sidescan sonar: images a horizontal region above the seafloor

Active Continental Margins

Where the oceanic lithosphere is being subducted beneath the continent (often associated with deep-ocean trenches)

Satellite radar altimeters can detect subtle changes (__ ____ ____) in elevation of the ocean surface

a few cm

Layer 1

consists of deep sea sediments and sedimentary rocks

Layer 4

consists of gabbro

Layer 3

consists of numerous interconnected dikes called a sheeted dike complex

Layer 2

consists of pillow lavas

5. Oceanic ridges with ______ spreading rates generally do not have a rift valley and have a shallow profile

fast

Newly formed melt (seafloor spreading)

from decompression melting of the mantle (slowly rises toward the surface)

Most melt solidifies in the ________ _________, but some escapes to the sea floor and erupts as lava

lower crust

the HMS Challenger expedition measured the depth of the seafloor by?

lowering weighted lines overboard - (Deepest spot measured is now called the Challenger Deep » 10,994 m deep, Measured in 1875)

Mapping the ocean floor from space using satellites equipped with?

radar altimeters

Ocanic crust forms as: Magma ascends through these fractures, cools, and solidifies to form a __________ ______ _________.

sheeted dike complex

3. Oceanic ridges with _______ spreading rates have well-developed rift valleys and rugged topography

slow

What is the evoulution of an ocean basin?

starts with the formation of a contineitail rift

subduction erosion is effective when the angle of desent is __________.

steep

Mixtures of sediment and water carried down ____________ __________.

submarine canyons

When the lithosphere is thick and cold

(rifts are narrow) Examples 1. East African Rift 2. Rio Grande Rift 3. Baikal Rift 4. Rhine Valley

When the lithosphere is thin and hot

(the rift can be very wide) Examples 1. Basin and Range in the western United States

Atlantic ocean

1. After tens of millions of years, the Red Sea will develop into a feature similar to the Atlantic Ocean 2. As new oceanic crust was added to the diverging plates, the rifted margins moved further from the region of upwelling 3. These margins cooled and subsided below sea level - Eventually become passive continental margins

How does Ocenaic crust form?

1. Basaltic magma originates from partially melted mantle peridotite 2. The magma rises through the upper mantle in tiny cracks until it reaches a lens-shaped magma chamber beneath the ridge crest 3. As the pressure in the chamber increases, the rock about the chamber periodically fractures

What are the 3 major areas of the ocean floor based on topography

1. Continental margins 2. Deep ocean basins 3. Oceanic ridges

East African Rift

1. Continental rift extending through eastern Africa 2. Consists of several interconnected rift valleys 3. Normal faulting led to grabens (down-faulted blocks) 4. Area has expensive basaltic flows and volcanic cones

what are some example of volcanic islands

1. Easter Island 2. Tahiti 3. Bora Bora 4. Galapagos Islands

Abyssal Plains

1. Flat features of the ocean floor (Likely the most level places on Earth) 2. Sites of thick accumulations of sediment (Fine sediments from turbidity currents) (Minerals precipitated from seawater) (Shells of marine plankton) 3. Found in all oceans (Most extensive in the Atlantic Ocean)

Red sea

1. Formed when the Arabian Peninsula rifted from Africa beginning about 30 million years ago 2. Fault scarps surrounding the Red Sea are similar to structures seen in the East African Rift 3. If spreading continues, the Red Sea will grow wider and develop an elongated mid-ocean ridge

Passive Continental Margins

1. Geologically inactive regions (not associated with plate boundaries) 2. Found along most coastal areas that surround the Atlantic Ocean 3. Experience little volcanism and few earthquakes

Characteristic of oceanic ridge, or mid-ocean ridge, or rise

1. The longest topographic feature on Earth 2. Width varies from 1000 to 4000 km 3. Occupy elevated positions 4. Segments are offset by transform faults 5. Extensive faulting and earthquakes

Characteristics of a continental shelf

1. Varies greatly in width 2. Gently sloping (average one-tenth of a degree slope) 3. Contains important mineral and oil deposits 4. Some areas contain extensive glacial deposits 5. Some areas contain shelf valleys 6. Important fishing grounds

What are two things associated with volcanic activity?

1. Volcanic islands arcs 2. Contenintal volcanic arcs (mostly found in pacific ocean)

Modern are the 2 bathymetric techniques

1. bathymetry 2. sonar

___-___ percent of the magma reaches the seafloor, where it quickly solidifies, forming large tube-shaped protuberances known as ________ ________

10-20% Pillow Basalts

From _____ to ____, the HMS Challenger expedition collected oceanographic data.

1872 to 1876

rift valleys range in width from ___ to ___ km and can have walls

30 to 50 km

How many layers make up the ophiolite complex?

4 layers

Only about ___% of the seafloor has been mapped in detail

5%

rift valleys tower from ____-_____ m abouve the valley floor

500-2500 m

Deep ocean basins

Between the continental margins and the oceanic ridge

What is the deepest spot in the ocean

Challenger Deep, in Mariana trench (10,994 meters below sea level) surface expression of a subduction zone

Seafloor spreding was formulated in the early 1960s by?

Harry Hess

Deep Ocean trench

Long narrow creases that represent the deepest part of the seafloor

Interactions between seawater and oceanic crust

Permeable and highly fractured crust allows seawater to penetrate the crust by 2-3 km

Massive underwater structures exert ________________ ______ _________ gravitational attraction (Water piles up over these features)

Stronger than normal

Guyots

Submerged, flat-topped seamounts 1. After the volcano is extinct, it eventually erodes to sea level where waves flatten the top of the structure 2. As plates carry the structure away, it eventually sinks into the ocean

Bathymetry

The topography (shape) of the ocean floor

(Active Continental Margins) Sediments and rocks can be scraped from the descending plate and accumulate on the continental plate as an_____________ ________.

accretionary wedge

Hot groundwater dissolves ions of various metals from the rock and precipitates them on the seafloor as particle-filled clouds called _______ _________

black smokers

When a turbidity current emerges onto the relatively flat ocean floor, the sediments spread out in a fan shape called a _______-____ _____. (the continental rise is composed of multiple deep-sea fans)

deep-sea fan

Early bathymetric profiles were created using _______ ________-, which bounce a sound off an object to determine the distance

echo sounders

Seawater is heated as it circulates through the crust, altering the basalt by ______________ __________________.

hydrothermal metamorphism

High-resolution multibeam

instruments send out a fan of sound and record reflections from various receivers to provide a more detailed view of the ocean floor (Produced first photograph-like images of seafloor)

4. Oceanic ridges with ___________ spreading rates have subdued rift valleys and topography

intermediate

Ophilite complex

is The sequence of four layers composing the oceanic crust is called an ophiolite complex

Continental shelf

is a gently sloping, flooded portion of the continent

Conternintrial slope

is a steep structure that marks the boundary between the continental and oceanic crust (Inclination average is 5 degrees) (The slope can reach 25 degrees)

Conternintial rise

is a thick accumulation of sediment from the continental slope

A continental rift

is an elongated depression where the lithosphere is stretched and thinned

Ocenaic ridge toporgraphy 1. Newly created Lithopshere-

is hot and less dense than surrounding rocks

2. As the newly formed crust moves away from the spreading center.

it cools and increases in density

An oceanic ridge, or mid-ocean ridge, or rise is a broad is a

linear swell along a divergent plate boundary

Subduction erosion

occurs when the subducting plate scrapes the bottom of the overriding plate

Where are most continental margins primarily located around?

the Pacific Ocean

Seaflor sreading accurs along?

the crest of ocenaic ridges

What are the two types of continental rifts? lithosphere that is

thick and cold thin and hot

sediments from continental rise are carried by?

turbiditary currents

Sonar

using sound energy, is now used to measure the depth to the ocean floor