Folds and faults

Tilted and folded sedimentary beds exposed at The Settlands coast. — Folded strata at The Settlands, Wales. Trace a bed through the exposure to see deformation recorded in solid rock.

A suggested lesson sequence

Use these stages at your own pace. Pause for students to sketch, compare observations or lead part of the demonstration.

01
Observe
Choose Anticline and identify the oldest bed. Compare Syncline; explain why age and shape are different criteria.
Open Observe
02
Tinker
Choose Normal fault and name hanging wall before playing. Reverse the sense of slip with Reverse fault, then compare lateral displacement in Strike-slip.
Open Tinker
03
Explain
Use the movement of the hanging wall to distinguish a normal fault from a reverse fault.
Open Explain
04
Check
Choose an answer and explain your reasoning. Each question includes feedback.
Open Check

Rehearse with the model

The same scene and controls as the lab. Load it when you are ready; use Start projector for the full classroom view.

Before the lesson

Compare the rock deformation caused by compression, tension and sideways motion, using folds and faults as evidence.

Open the model before the lesson and choose a view that makes the important feature easy to see. Drag to rotate, and use the on-screen controls to change one variable at a time. The Controls panel explains the available keyboard shortcuts.

Pause the animation at a useful moment. Ask students what should happen next, then play it to test their explanation.

Guide the demonstration

Choose Anticline and identify the oldest bed. Compare Syncline; explain why age and shape are different criteria.

Choose Normal fault and name hanging wall before playing. Reverse the sense of slip with Reverse fault, then compare lateral displacement in Strike-slip.

Discuss a common misconception

“The hanging wall is always the side of a fault that moves down.” The hanging wall is defined by its position above an inclined fault plane. It moves down relative to the footwall in a normal fault and up in a reverse fault. Identify the plane and blocks before using their displacement to name the fault type.

Build the explanation

Rock layers may bend into folds or break and move along faults. Layer age, orientation and relative movement help distinguish structures that can look similar from one viewing angle.

Choose Normal fault and name hanging wall before playing. Reverse the sense of slip with Reverse fault, then compare lateral displacement in Strike-slip.

The deformation is prescribed to reveal structure; it does not solve rock failure or the stresses at a particular site.

Teaching notes

Identify the hanging wall and footwall from their positions relative to the fault plane before describing movement.

Explain how rock can deform over geological time; a soft classroom material only helps visualise the resulting shape.

Distinguish horizontal movement along the San Andreas system from subduction at Cascadia.

Check understanding

Open Check for 4 questions. Ask students to explain their choice before revealing the answer.

Return to the opening photograph. Ask students to identify one visible feature and explain which part of the model helps account for it.

Look more closely

Use these observations to connect the vocabulary to features students can identify.

Normal fault

Steep dark rock walls border the Almannagjá rift at Þingvellir, Iceland. — Almannagjá, Þingvellir: faults accommodate extension within Iceland's broad North American–Eurasian plate boundary zone.

Read the definition

Reverse fault