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The sartorial spendour of spiny Murex – the real show-offs in the world of gastropods. From the left: Chicoreus ramosus (the Ramose Murex, Philippines); Murex pecten (Venus comb Murex, Philippines); Porieria zelandica (New Zealand) – the one I stood on!.
The sartorial splendour of spiny Murex – the real show-offs in the world of gastropods. From the left: Chicoreus ramosus (the Ramose Murex, Philippines); Murex pecten (Venus comb Murex, Philippines); Porieria zelandica (New Zealand) – the one I stood on!.

374 articles, atlases, and glossaries to choose from
Herein you will find posts on Earth and planetary sciences, Art and Science and other digressions that focus on Science Communication and online resources for students of all disciplines, but particularly Geology. Post categories-topics are linked to the navigation bar or just head to the latest additions listed below.

I do this for the love of it. I do not receive any remuneration for the site (and I don’t advertise). The website (geological-digressions.com) is not attached or beholden to any organization.

A number of colleagues have kindly donated images for certain categories of posts. They are all acknowledged, usually in the caption to an image. They are also acknowledged in a Contributors Page.

The How to… articles are designed for geology students, providing outlines of method and theory for some of the basic tasks that geologists undertake in the field and lab. They are directed primarily at beginning and undergraduate geology students and anyone else wanting a reminder or primer, and as such are a bit more technical than other posts.

Peruse the Atlas series for images of different geological environments and processes, modern and ancient.

The Glossary has been compiled from terms used in this website. Links to the relevant posts are included. There are currently 11 glossaries.

And finally, if you would like to know something about me, where I’ve come from, where I’ve been – A geological life

If you use any of the images on this website, please follow the normal protocols for attribution – for example: Brian Ricketts or Geological Digressions followed by the article link/URL.

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Conjugate fractures and en echelon tension gashes – indicators of brittle failure in Old Red Sandstone, Gougane Barra, County Cork, Ireland.
Mohr-Coulomb failure criteria
April 3, 2024
A montage of stress transformation paraphernalia and rock deformation
Mohr circles and stress transformation
March 23, 2024
The Marlborough strike-slip fault array extends north from the dextral Alpine Fault transform; faults continue across Cook Strait to join the North Island Dextral Fault Belt in the Wellington region (central Aotearoa New Zealand). In Marlborough and beneath Cook Strait there are several pull-apart basins formed at releasing bend stepovers. Sandbox analogue models can help us decipher the mechanical and kinematic processes that produce structures like these. Base image from NASA – International Space Station 2003.
Strike-slip analogue models
March 12, 2024
Scaled sand-box experiments are an ideal medium to observe rock deformation that, in this example, involves synkinematic deposition during rift-like crustal extension. The choice of model materials, in addition to imposed boundary conditions such as strain rates, will determine the outcome of the experiment. Dry sand was chosen for this model because its brittle behaviour under the model conditions is a good representation of natural rock failure. Diagram modified slightly from Eisenstadt and Sims, 2005, Figure 3a.
Analogue structure models: Scaling the materials
February 21, 2024
The relationship between inertial and gravitational forces expressed by the Froude number (Fr) is reflected by the changes in surface flows and the formation-decay of stationary (standing) waves. Fr < 1 reflects subcritical (tranquil) flow; Fr>1 supercritical flow. Although the Froude number can be determined experimentally, it can also be eased out of a dimensional analysis of the relevant hydrodynamic variables.
Model dimensions and dimensional analysis
February 2, 2024
Recent Posts
Conjugate fractures and en echelon tension gashes – indicators of brittle failure in Old Red Sandstone, Gougane Barra, County Cork, Ireland.
Mohr-Coulomb failure criteria
April 3, 2024
A montage of stress transformation paraphernalia and rock deformation
Mohr circles and stress transformation
March 23, 2024
The Marlborough strike-slip fault array extends north from the dextral Alpine Fault transform; faults continue across Cook Strait to join the North Island Dextral Fault Belt in the Wellington region (central Aotearoa New Zealand). In Marlborough and beneath Cook Strait there are several pull-apart basins formed at releasing bend stepovers. Sandbox analogue models can help us decipher the mechanical and kinematic processes that produce structures like these. Base image from NASA – International Space Station 2003.
Strike-slip analogue models
March 12, 2024
Scaled sand-box experiments are an ideal medium to observe rock deformation that, in this example, involves synkinematic deposition during rift-like crustal extension. The choice of model materials, in addition to imposed boundary conditions such as strain rates, will determine the outcome of the experiment. Dry sand was chosen for this model because its brittle behaviour under the model conditions is a good representation of natural rock failure. Diagram modified slightly from Eisenstadt and Sims, 2005, Figure 3a.
Analogue structure models: Scaling the materials
February 21, 2024
The relationship between inertial and gravitational forces expressed by the Froude number (Fr) is reflected by the changes in surface flows and the formation-decay of stationary (standing) waves. Fr < 1 reflects subcritical (tranquil) flow; Fr>1 supercritical flow. Although the Froude number can be determined experimentally, it can also be eased out of a dimensional analysis of the relevant hydrodynamic variables.
Model dimensions and dimensional analysis
February 2, 2024

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