Geology 14 (The Ocean Floor)

Earth and Space Sciences X

29 Oct 201538:33

EducationalLearning

32 Likes 10 Comments

TLDRThe video discusses the geology of the ocean floor. It describes the main features and structures like continental shelves, submarine canyons, trenches, ridges and rifts. It explains how sea floor spreading at mid-ocean ridges creates new oceanic crust while old crust is destroyed at subduction zones. The summary covers topics like seamounts, abyssal plains, hydrothermal vents, ocean formation through continental rifting, and the life cycle of oceanic plates.

Takeaways

😀 The ocean floor has 3 major provinces: continental margins, deep ocean basins, and mid-ocean ridges
🌊 Passive continental margins have features like submarine canyons and deep sea fans
🌊 Active margins have trenches where oceanic plates are subducting under continental plates
🌊 Abyssal plains are very flat regions between continental margins and mid-ocean ridges
🔥 Mid-ocean ridges are the largest topographic feature on Earth, formed by seafloor spreading
😮 Rift valleys can form along slow spreading mid-ocean ridges like in Iceland
🌋 Fast spreading ridges lack rift valleys and have extensive volcanic activity
💧 Hydrothermal vents called black smokers precipitate minerals on the seafloor
🌉 Continental rifts can split continents and create new ocean basins over time
😀 Oceanic lithosphere is recycled every ~180 million years as plates are created and destroyed

Q & A

What are some key features of the ocean floor?
-The ocean floor has three major provinces - the continental margins, the deep ocean basins, and the oceanic mid-ocean ridges. It also contains features like submarine canyons, seamounts, abyssal plains, and hydrothermal vents.
How are passive and active continental margins different?
-Passive margins have a gentle slope from the continental shelf to the deep ocean basin. Active margins descend abruptly into a deep ocean trench as the oceanic plate subducts under the continental plate.
What causes the elevated topography of mid-ocean ridges?
-New oceanic lithosphere formed at mid-ocean ridges is hot and less dense, so it sits higher than the surrounding colder ocean floor. As it moves away from the ridge, it cools, becomes denser, and sinks lower.
What is seafloor spreading and how does it work?
-Seafloor spreading occurs at mid-ocean ridges. As tectonic plates diverge, magma upwells into the gap, generating new oceanic lithosphere. The new material moves away from the ridge like a conveyor belt.
How does the oceanic crust form layers?
-The oceanic crust forms four main layers from top to bottom - unconsolidated sediments, pillow basalts, sheeted dikes from magma injection, and gabbro from the magma chamber.
What are hydrothermal vents and black smokers?
-As seawater circulates through the fractured ocean crust, it heats up and dissolves minerals. When this hot mineral-rich water vents back into the ocean, the minerals precipitate out as black smoke-like plumes called black smokers.
How do new oceans form?
-New oceans form when continents rift apart. A continental rift valley lengthens and deepens, eventually splitting the continent and allowing seafloor spreading to occur.
What causes oceanic lithosphere to subduct?
-Old, dense oceanic lithosphere can spontaneously subduct under its own weight at a steep angle. Young oceanic lithosphere can be forced to subduct at shallower angles due to compressional forces.
How do oceanic plates disappear over time?
-Oceanic plates are eventually recycled back into the mantle through subduction. As the plates shrink, they may disconnect into smaller fragments before completely disappearing.
How did the San Andreas Fault form?
-The San Andreas Fault formed along the old subduction zone boundary after the Farallon plate was completely subducted beneath North America. It accommodates transform motion between the Pacific and North American plates.

Outlines

00:00

🎬 Introducing the ocean floor and its mysteries

The ocean floor covers most of Earth but is difficult to study due to its remoteness and darkness. It has three main provinces: continental margins, deep ocean basins, and the mid-ocean ridge. The Atlantic Ocean exemplifies the main features of the global ocean floor.

05:04

😊 Describing the structure of passive continental margins

Passive continental margins have a shelf, slope, and rise. They lack trenches but have faults stepping down into the oceanic crust. They can contain oil, glacial deposits, canyons distributing sediment as fans, and mark the oceanward edge of the continental crust.

10:04

🌋 Contrasting active margins with their trenches and volcanoes

Active continental margins descend abruptly into ocean trenches at subduction zones. Sediment and crustal scrapings accumulate in accretionary wedges. Trenches are narrow, include the deepest ocean points, and associate with volcanic activity as oceanic crust is forced down.

15:08

🌎 Introducing abyssal plains: The great underwater flatlands

Abyssal plains are very flat, deep seafloor regions accumulating thick sediments from turbidity currents. They occur worldwide in all oceans, especially beneath fans deposited from continental shelves.

20:10

🔥 Discussing mid-ocean ridges and their volcanic activity

Mid-ocean ridges are the largest topographic feature on Earth at 43,000 miles long. They exhibit extensive volcanic and tectonic activity in narrow rift zones, creating new ocean crust in a conveyor belt fashion along divergent plate boundaries.

25:13

💧 Explaining hydrothermal alteration of ocean crust by water

Seawater circulates down through the permeable, fractured ocean crust, altering the basalts. Hot hydrothermal fluids leach metals that precipitate as "black smoker" particle plumes when the mineral-laden water exits at vents.

30:15

➕ How continental rifts can birth new oceans over time

As with the Red Sea and Gulf of Aden, ocean basins begin forming when continental rifts split landmasses. With continued extension, ridges and passive margins develop to generate new oceans, as between Africa and South America.

35:16

📉 Discussing the life cycle of oceanic tectonic plates

Oceanic lithosphere descends by spontaneous sinking at steep angles when dense and old or by shallower, forced subduction when younger. Plates can shrink over tens of millions of years, as exemplified by the consumed Farallon plate, replaced by the San Andreas fault.

Mindmap

Keywords

💡ocean floor

The ocean floor refers to the bottom surface of the ocean basins. It covers around 71% of the Earth's surface. In the video, the narrator talks extensively about the various features and geology of the ocean floor, like the mid-ocean ridges, trenches, seamounts, abyssal plains, etc. He notes that we know less about the ocean floor compared to the surface of other planets like Mars, due to the challenges of exploring the depths of the oceans.

💡continental margin

The continental margins refer to the zone where the continents meet the oceans. They consist of the continental shelf, continental slope and continental rise. In the video, the narrator explains the structure of passive continental margins, noting they are found where trenches are absent and often contain important mineral deposits like oil.

💡mid-ocean ridges

The mid-ocean ridges are the most extensive mountain ranges on Earth, spanning over 43,000 miles across all major ocean basins. They are formed by seafloor spreading at divergent plate boundaries. The video discusses their structure, including rift valleys, and how they produce new oceanic crust.

💡seafloor spreading

Seafloor spreading is the process by which new oceanic lithosphere or crust is formed along mid-ocean ridges as tectonic plates move apart. It was formulated by Harry Hess in the 1960s. The video explains how it creates new ocean floor through upwelling magma and conveys crust in a conveyor belt fashion.

💡abyssal plain

Abyssal plains are vast flat areas of the ocean floor covered in thick sediments. As noted in the video, they are some of the flattest regions on Earth and are found between the continental margins and mid-ocean ridges in all ocean basins.

💡hydrothermal vents

Also called black smokers, hydrothermal vents form where seawater circulates through fractured ocean crust, dissolving minerals that then precipitate on the seafloor as particle clouds. The video explains how they are created by the interaction between seawater and hot oceanic crust.

💡subduction

Subduction is the process where oceanic lithosphere sinks beneath another tectonic plate and back into the mantle at convergent plate boundaries. The video contrasts spontaneous versus forced subduction, noting factors like lithosphere density and age.

💡accretionary wedge

As oceanic crust subducts, scraped off sediments and crust accumulate to form accretionary wedges along the trenches. The video notes they extend the edge of the continents and contain minerals.

💡continental rifting

Continental rifting is the initial splitting of continents that can eventually form new oceans, as discussed in the video using the examples of the East African Rift and the breakup of Africa and South America.

💡Farallon plate

The Farallon plate was a tectonic plate in the Pacific Ocean that has now mostly subducted below North America. The video uses it as an example of how oceanic plates come and go over geologic timescales.

Highlights

Researchers developed a new method for detecting gravitational waves using laser interferometry.

The LIGO observatory enabled the first direct detection of gravitational waves in 2015.

Gravitational waves provide a new way to observe the universe and test general relativity.

The merger of two black holes produced the first detected gravitational waves.

Gravitational wave detection opens up a new field of gravitational wave astronomy.

The waveform signature of detected gravitational waves matched predictions from general relativity.

These gravitational wave observations allow unprecedented tests of general relativity.

The detection helps address unsolved mysteries about black holes and neutron stars.

The researchers discuss future directions like space-based gravitational wave detectors.

The sensitivity of current detectors is constantly being improved.

Deeper understanding of gravitational waves could lead to new physics and cosmology.

The discoveries open up new avenues for studying merging black holes.

The ability to detect gravitational waves enables multimessenger astronomy.

This technology will allow observation of millions of new cosmic events.

The researchers emphasize the importance of open data sharing in this field.

Transcripts

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