earth science

Louisville Ridge

Louisville Ridge is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Louisville Ridge rather than just read about it. In short: The Louisville Ridge, often now referred to as the Louisville Seamount Chain, is an underwater chain of over 70 seamounts located in the Southwest portion of the Pacific Ocean. One of the longest seamount chains on Earth, it stretches some 4,300 km (2,700 mi) from the Pacific-Antarctic Ridge northwest to the Tonga-Kermadec Trench, where it subducts under the Indo-Australian Plate as part of the Pacific Plate.

Key takeaways

Louisville Ridge belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Louisville Ridge to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Louisville Ridge from memory before moving on to harder problems.

Reference excerpt

The Louisville Ridge, often now referred to as the Louisville Seamount Chain, is an underwater chain of over 70 seamounts located in the Southwest portion of the Pacific Ocean. One of the longest seamount chains on Earth, it stretches some 4,300 km (2,700 mi) from the Pacific-Antarctic Ridge northwest to the Tonga-Kermadec Trench, where it subducts under the Indo-Australian Plate as part of the Pacific Plate. The chain's formation is best explained by movement of the Pacific Plate over the Louisville hotspot, although others have suggested that it formed by leakage of magma from the shallow mantle up through the Eltanin fracture zone, which it follows closely for some of its course. Depth-sounding data first revealed existence consistent with a seamount chain in 1972, although some of the seamounts had been described as a ridge in 1964 linked to the Eltanin fracture zone system, hence the name.

Geology

The oldest volcanic rocks of the chain come from Osbourn Seamount at 78.8 ± 1.3 Ma; ages become younger in a nonlinear fashion towards the southeast, with a youngest age of 1.1 Ma. Composition studies of the erupted dominantly alkali basalt are consistent with a single Louisville mantle source distinct from other hotspots, and the composition has remained homogeneous over at least the last 70 million years. In the past 25 million years, magma upwelling rates may have decreased. There is almost certainly a deep plume origin to the hotspot. The Louisville hotspot chain passes through the western and eastern branches of the Wishbone scarp, and while the seamounts show no compositional change as they cross the scarps, the East Wishbone scarp crossing point is associated with a distinct decrease in the volume of the younger seamount eruptives from that point east into the Pacific Plate.

Tectonics Volcanic hotspot chains are used to suggest the net movements of tectonic plates, and so in the case of the large Pacific Plate, validation of models of its movement and indeed the hotspot hypothesis itself relies on data from several hot spot chains. As well as the Louisville hotspot, there is data over tens of millions of years available from the movements of the Hawaii hotspot and the Arago hotspot. While the model of Pacific Plate movement, including bends in the hotspot track, can be made to fit very well, there has been long debate on the timings of such bends as mismatches of a few million years appeared to exist.

Subduction The area of subduction of the Louisville chain into the Tonga Trench is associated with a relative seismic gap beneath the Tonga forearc. This implies that the subduction of the volcanoes compared to normal sediment has a significant impact in terms of normal relief of stress, but it is unclear if the subducted volcanoes relieve it as suggested by some or increase the potential for sudden release. Further, a postulated historic change in the trend of the subducted Louisville chain compared to present is backed up by compositional analysis of more recent arc volcanism as the volcanics from the Louisville chain are recycled. A bathymetric high c. 2 km (1.2 mi) northwest of the Osbourn Seamount has been interpreted as the currently subducting portion of the Louisville chain, but this continuation is not aligned with the extant chain.

Ecology Some of the seamounts are known coral reef stoney habitats, with typical species including the coral Solenosmilia variabilis, brisingid starfishes (Order Brisingida), and sea-lilies and feather stars (Class Crinoidea). They can be a fishery resource for species such as the orange roughy (Hoplostethus atlanticus) that can be fished by bottom trawling.

Seamounts The Louisville Ridge includes the following:

See also Louisville hotspot Hollister Ridge Hotspot (geology) Zealandia

References

Sources

External links Expedition 330 - Louisville Seamount Trail, Integrated Ocean Drilling Program, 13 December 2010 to 11 February 2011 The Louisville Ridge – Tonga Trench collision: Implications for subduction zone dynamics, RV Sonne Research Expedition SO215 Cruise Report, 25 April 2011 to 11 June 2011

Illustrations

Worked examples

Example 1 — a first encounter with Louisville Ridge

Start with the simplest possible case. Write down what Louisville Ridge claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Louisville Ridge before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Louisville Ridge ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Louisville Ridge

In research: Louisville Ridge appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Louisville Ridge in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Louisville Ridge is common in secondary-school and first-year university syllabi. It links to neighbouring topics Guyots, Hotspot tracks, Oceanography, so understanding it makes those chapters shorter.
In everyday life: Look for Louisville Ridge outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Louisville Ridge in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Louisville Ridge means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Louisville Ridge out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Louisville Ridge in simple terms?

Why does Louisville Ridge matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Louisville Ridge?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Louisville Ridge.