When Rocks Bend

The rocks exposed in this roadside rock cutting were originally deposited as nearly horizontal layers on the floor of an ancient sea more than 400 million years ago. During a later mountain-building event, powerful compressional forces squeezed these layers together, causing them to bend into an arch known as an anticline. Instead of remaining straight, the rock layers curve through the fold while remaining continuous, showing that they bent rather than broke. This type of deformation is known as ductile deformation and occurs deep within the Earth's crust, where high temperatures and pressures allow rocks to slowly change shape over millions of years.

Although millions of years of uplift and erosion gradually brought these folded rocks closer to the Earth's surface, the anticline would remain largely hidden beneath soil and vegetation if not for the construction of this roadside rock cutting. The excavation provides a remarkable cross-sectional view through the fold, allowing its internal structure to be seen clearly. Look closely and you'll also notice a small fault on the left-hand side of the exposure. This formed after the rocks had been uplifted and cooled, when they had become more brittle and fractured under continued tectonic stress. Together, the anticline and fault preserve evidence of two different ways rocks respond to stress—first by bending, then by breaking.

If you want to know about how these features are measured and classified, see the nearby "Anyone for a dip?" (GC4QEPH) by micaparamedic

Logging Tasks

1. Standing in front of the roadside rock cutting, observe the folded rock layers. Describe the overall shape of the fold and identify approximately where the hinge (the highest point of the anticline) is located within the exposure.

2. Choose one clearly visible rock layer and visually follow it across the outcrop. Describe how its direction changes as it passes through the fold. How does your observation support the explanation that the rocks bent rather than broke when the anticline formed?

3. Take a selfie (or something that identifies you) that includes the geological feature. This can go in your log, or if you prefer, you can send it to me alongside your answers.

You may log your find immediately after completing the EarthCache. Please message your answers as soon as possible. If your answers are not received within approximately 14 days, your find log may be deleted.