- Related Topics:
- continental landform
- volcanism
aseismic ridge
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What is an aseismic ridge?
An aseismic ridge is a long, mountainous structure on the ocean floor, characterized by an absence of earthquakes, which distinguishes it from oceanic spreading centers. These ridges are mainly formed by volcanism from a hot spot, creating coalescing volcanoes. The Hawaiian-Emperor chain is a prime example, marked by volcanic activity at its southeastern end on the island of Hawaii.
Other notable aseismic ridges include the Ninetyeast Ridge in the Indian Ocean, believed to originate from hot spot volcanic activity at the Kerguelen Islands near Antarctica, and the Walvis Ridge in the South Atlantic. The Ninetyeast Ridge stretches 4,500 kilometers from the Andaman Islands to Broken Ridge.
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How is an aseismic ridge different from a volcanic ridge?
Aseismic ridges and volcanic ridges both have a mountainous, linear structure that rises from the ocean floor and are created by volcanism. The key difference lies in their seismic activity; aseismic ridges do not experience earthquakes, which distinguishes them from volcanic ridges located at oceanic spreading centers. Most aseismic ridges are formed by hot spot volcanism, where chains of coalescing volcanoes create the structure. An example is the Hawaiian-Emperor chain, which only experiences earthquakes at its active volcanic end, near the island of Hawaii.
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Where are aseismic ridges usually found on Earth?
Aseismic ridges are long, linear, mountainous structures on the ocean floor, distinguished from oceanic spreading centers by the absence of earthquakes.
Most aseismic ridges are formed by volcanism from a hot spot and consist of coalescing volcanoes. Examples include the Hawaiian-Emperor chain in the northwest Pacific, the Ninetyeast Ridge and the Chagos-Laccadive Plateau in the Indian Ocean, and the Walvis Ridge and Rio Grande Rise in the South Atlantic.
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How are aseismic ridges formed?
Aseismic ridges are extensive, linear, mountainous structures that stretch across the floor of some ocean basins. The majority of aseismic ridges are formed by volcanism from a hot spot and comprise merging volcanoes of varying sizes. A feature that differentiates aseismic ridges from oceanic spreading centers is that earthquakes do not occur within them.
The Hawaiian-Emperor chain is the most well-known aseismic ridge. Other prominent aseismic ridges include the Ninetyeast Ridge and the Chagos-Laccadive Plateau in the Indian Ocean, as well as the Walvis Ridge and Rio Grande Rise in the South Atlantic.
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What are some well-known examples of aseismic ridges?
An aseismic ridge is a long, linear, mountainous structure on an ocean basin floor that does not experience earthquakes.
Well-known examples of aseismic ridges include:
* The Hawaiian-Emperor chain, which stretches from the island of Hawaii to the intersection of the Kuril and Aleutian trenches in the northwest Pacific.
* The Ninetyeast Ridge in the Indian Ocean, which stretches from the Andaman Islands to where it intersects Broken Ridge.
* The Walvis Ridge in the South Atlantic, which trends northeast from the islands of Tristan da Cunha to the African margin.
* The Rio Grande Rise in the South Atlantic, which trends southeast from the South American margin toward the Mid-Atlantic Ridge.2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
Why are aseismic ridges important to scientists studying plate tectonics?
Aseismic ridges are significant to scientists studying plate tectonics because they offer insights into the movement of plates and the processes that drive them. These ridges, unlike oceanic spreading centers, do not experience earthquakes, which distinguishes them.
Most aseismic ridges are formed by volcanism from a hot spot, creating a chain of coalescing volcanoes. The Hawaiian-Emperor chain is a prime example, illustrating how changes in the direction of plate motion can be inferred from the ridge's trend. By studying aseismic ridges and using techniques like seismic tomography, scientists can understand plate-driving mechanisms and the composition of Earth's interior.
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aseismic ridge, a long, linear and mountainous structure that crosses the basin floor of some oceans. Earthquakes do not occur within aseismic ridges, and it is this feature that distinguishes them from oceanic spreading centres. Most aseismic ridges are constructed by volcanism from a hot spot and are composed of coalescing volcanoes of various sizes.
The Hawaiian-Emperor chain is the best displayed aseismic ridge. Earthquakes do occur there, but only at the end of the ridge where volcanism is current—in this case, on the island of Hawaii (commonly known as the Big Island) to the southeast end of the island chain. Taking into account the relief of the island of Hawaii above the seafloor, it is the largest volcanic edifice on Earth. The Hawaiian-Emperor chain stretches from the Big Island to the intersection of the Kuril and Aleutian trenches in the northwest Pacific. There are roughly 18 volcanoes or seamounts per 1,000 kilometres (about 600 miles) along the Hawaiian segment and 13 per 1,000 kilometres on the Emperor portion beyond the bend. The Hawaiian Islands are a part of the chain—the young part—that rises above sea level. The Hawaiian-Emperor chain has two main trends: (1) from the Hawaiian Islands west to the Kammu and Yūryaku seamounts (near 32° N, 168° W), the trend of the Hawaiian portion is just west of northwest; and (2) from this point to the Aleutian Trench, the trend of the Emperor segment is north-northwest. The hot spot interpretation infers that this change in trend is due to a change in the direction of Pacific Plate motion, from north-northwest prior to 38 million years ago (the age of the ridge at the change in trend) to west of northwest until the present day. Radiometric dating of rocks from the ridge indicates that it is 70 million years old at its extreme north end.
Other prominent aseismic ridges include the Ninetyeast Ridge and the Chagos-Laccadive Plateau in the Indian Ocean and the Walvis Ridge and Rio Grande Rise in the South Atlantic. The Ninetyeast Ridge is thought to have originated from hot spot volcanic activity now located at the Kerguelen Islands near Antarctica. These islands lie atop the Kerguelen Plateau, which also originated from volcanism at this hot spot. The Ninetyeast Ridge stretches parallel to 90° E longitude in a long, linear chain of seamounts and volcanic ridges from the Andaman Islands in the Bay of Bengal more than 4,500 kilometres (2,800 miles) to the south where it intersects Broken Ridge at 30° S latitude. Broken Ridge is an aseismic ridge and was once part of the Kerguelen Plateau. It was split away from the plateau as Australia separated from Antarctica.
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Core samples of the seafloor along the Ninetyeast Ridge have been retrieved through deep-sea drilling. Analyses of the samples show that the ridge is slightly less than 30 million years old in the south and about 80 million years old in the north. Additionally, sediments on the ridge indicate that parts of it were above sea level while it was being built near a spreading centre. The ridge then subsided as it rode north on the Indian Plate.
The Walvis Ridge and Rio Grande Rise originated from hot spot volcanism now occurring at the islands of Tristan da Cunha 300 kilometres (about 190 miles) east of the crest of the Mid-Atlantic Ridge. The Walvis Ridge trends northeast from this location to the African margin. The Rio Grande Rise trends roughly southeast from the South American margin toward the Mid-Atlantic Ridge. Both the Walvis Ridge and Rio Grande Rise began forming from the same hot spot near the spreading centre as the South Atlantic was in its initial opening stages 100 to 80 million years ago. The spreading centre shifted west of the hot spot about 80 million years ago, ending construction of the Rio Grande Rise but continuing to build the Walvis Ridge. Volcanic activity has since diminished, resulting in the younger part of the latter ridge being smaller. The findings of ocean drilling on the Rio Grande Rise show that it was once a volcanic island some two kilometres (one mile) high.