earth science

Rheid

Rheid 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 Rheid rather than just read about it. In short: In geology, a rheid is a substance whose temperature is below its melting point and whose deformation by viscous flow during the time of observation is at least three orders of magnitude (1,000 ×) greater than the elastic deformation under the given conditions. A material is a rheid by virtue of the time of observation.

Key takeaways

Rheid 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 Rheid to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Rheid from memory before moving on to harder problems.

Reference excerpt

In geology, a rheid is a substance whose temperature is below its melting point and whose deformation by viscous flow during the time of observation is at least three orders of magnitude (1,000 ×) greater than the elastic deformation under the given conditions. A material is a rheid by virtue of the time of observation. The term, coined by S. Warren Carey in 1953, has the same Greek root as rheology, the science of viscoelasticity and nonlinear flow.

Types of rheids Almost any type of rock can behave as a rheid under appropriate conditions of temperature and pressure. For example, the Earth's mantle undergoes convection over long time-scales. As the mantle supports the propagation of shear waves, it may be deduced that it is a solid and, therefore, behaving as a rheid when it undergoes said convection. Granite has a measured viscosity at standard temperature and pressure of about 4.5×1019 Pa·s so it should be considered a rheid. Similarly halite, the mineral form of table salt, is a geological material that behaves as a rheid over relatively short time-periods. As salt is buried by other types of sediments, it will often flow laterally towards regions of lower confining stress. Through this mechanism, salt domes and other structures may form. In some areas, such as the Gulf of Mexico, these structures often serve as traps for petroleum and natural gas.

References

Worked examples

Example 1 — a first encounter with Rheid

Start with the simplest possible case. Write down what Rheid 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 Rheid 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 Rheid 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 Rheid

In research: Rheid 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 Rheid 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: Rheid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Structural geology, Structural geology stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Rheid 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 Rheid in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Rheid 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 Rheid out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Rheid in simple terms?

Why does Rheid 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 Rheid?

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 Rheid.