engineering

Hummocky cross-stratification

Hummocky cross-stratification is a engineering 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 Hummocky cross-stratification rather than just read about it. In short: Hummocky cross-stratification is a type of sedimentary structure found in sandstones. It is a form of cross-bedding usually formed by the action of large storms, such as hurricanes.

Key takeaways

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

Reference excerpt

Hummocky cross-stratification is a type of sedimentary structure found in sandstones. It is a form of cross-bedding usually formed by the action of large storms, such as hurricanes. It takes the form of a series of "smile"-like shapes, crosscutting each other. It is only formed at a depth of water below fair-weather wave base and above storm-weather wave base. They are not related to "hummocks" except in shape.

History The name was introduced by Harms et al. in 1975. Before this time, these structures were recognized under many different names. When hummocky cross-stratification was founded, it was originally given the name "truncated wave-ripple laminae", by Campbell (1966, 1971). The main features were listed by Bourgeois (1980), Harms et al. (1982), and Walker (1983), in order to identify the structure. Dott and Bourgeois launched an idealized hummocky stratification sequence. From bottom to top, these include: first-order scoured base (± sole marks); characteristic hummocky zone with several second-order truncation surfaces separating individual undulating lamina sets; a zone of flat laminae; a zone with well-oriented ripple cross-laminae and symmetrical ripple forms; all overlain by a more or less burrowed mudstone or siltstone. Walker (1983) wanted to create a second sequence, but it was decided that this sequence offers the best basis for studying hummocky cross-stratification for the future.

Composition This structure is commonly found in silt to fine sand. It is typically interbedded with bioturbated mudstone. It commonly contains concretions of abundant mica and plant detritus in the tops of many laminae. This helps indicate a shape sorting. Although hummocky cross-stratification is usually found in shallow marine sedimentary rocks, it has also been found in some lacustrine sedimentary rocks.

Common characteristics

In plan view (seen from above), it takes on the form of hummocks and swales that are circular to elliptical, with long wavelengths (1–5 m) but with low height (tens of centimeters). Laminations drape these hummocks; in cross-section view, these laminations have an upward curvature, and low angle, curved intersections. Hummocky cross-stratification can form in sediments up to about 3 cm in diameter, with near-bed water particle velocities between about 40–100 cm/s.

Formation of structure This structure is formed under a combination of unidirectional and oscillatory flow that is generated by relatively large storm waves in the ocean. Deposition involves fallout from suspension and lateral tractive flow due to wave oscillation. As the large waves drape sand over an irregular scoured surface, this strong storm-wave action erodes the seabed into low hummocks and swales that lack any significant orientation. It is usually formed by redeposition below normal fair weather wave base delivered offshore by flooding rivers and shoals by large waves.

Depositional environments During ancient times, hummocky cross-stratification was located in shallow marine environments, on the shore face and shelf by waves. It can also form on land during especially large storms when large amounts of water are pushed up onto the tidal flat. These landward deposits feature smaller bed forms due to the attenuation of storm waves as they move onto the land. While it is usually formed in marine settings by the action of storms (e.g.hurricane) it may also be deposited in fluvial strata; a fluvial origin is more likely if the unit solely comprises sand.

See also Wave base Sedimentary structures

References

Illustrations

Worked examples

Example 1 — a first encounter with Hummocky cross-stratification

Start with the simplest possible case. Write down what Hummocky cross-stratification claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, 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 Hummocky cross-stratification 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 Hummocky cross-stratification 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 Hummocky cross-stratification

In research: Hummocky cross-stratification appears in engineering 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 Hummocky cross-stratification 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: Hummocky cross-stratification is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cross-bedding, Sedimentary structures, Sedimentology, so understanding it makes those chapters shorter.
In everyday life: Look for Hummocky cross-stratification 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Hummocky cross-stratification” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Hummocky cross-stratification in 20 minutes

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

Frequently asked questions

What is Hummocky cross-stratification in simple terms?

Hummocky cross-stratification is a type of sedimentary structure found in sandstones. It is a form of cross-bedding usually formed by the action of large storms, such as hurricanes.

Why does Hummocky cross-stratification matter?

Because it connects several engineering 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 Hummocky cross-stratification?

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 Hummocky cross-stratification.