Internal and External Forces – Folding, Faulting, Erosion and Deposition
GeographyEarth's Structure & LandformsAges 15–16
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Earth's Structure & Landforms
A cross-section of Earth's crust with horizontal rock layers. Choose compression (two plates push together, folding rock into anticlines and synclines) or extension (rock fractures, forming horsts and grabens), then press Run: internal forces lift the terrain at a set rate in mm/year, while external forces — weathering and erosion — wear down the peaks and deposit material into low spots, building plains. Drag on the cross-section to raise or lower a section of crust yourself; the readout shows elapsed time, peak elevation, and the thickness of eroded and deposited material. The Deformation view shows compression folding layers into anticlines and synclines or breaking them along reverse faults, thrusts and nappes, tension making normal faults, horsts and grabens, and shear making strike-slip faults, with the hanging wall and footwall labelled. The Isostasy view floats crustal blocks on the denser mantle (Airy model), so erosion, deposition and ice loading or melting make the crust sink or rebound.
Lesson: Internal and external forces shaping Earth's surface relief
What it shows
Relief is shaped by internal forces, driven by energy inside the Earth, and by external forces such as weathering and erosion. Compression folds rock layers into anticlines and synclines or breaks them along reverse faults and low-angle thrusts that carry nappes; tension makes normal faults, horsts and grabens; shear makes strike-slip faults. Erosion wears the highs down, and when it matches the uplift rate the elevation levels off. The crust also floats on the denser mantle, so mountains have deep roots (Airy isostasy) and the land rebounds when ice melts or rock is eroded. The models are schematic.
How to use
In Internal & external forces, choose Compression or Extension, set the Internal force and External force sliders and press Run. In Deformation, pick a Structure, press Deform and read the shortening and the slip; then try New mystery section. In Isostasy, choose a Situation, tap a column and press Erode 1 km, Deposit 1 km, Add 1 km of ice or Melt all the ice, and watch the column sink or rebound.
Parameters you can change
- Internal force movement Compression (folding), Extension (faulting), Internal forces off
- Uplift rate from internal forces 0–10 mm/year
- External force intensity (erosion) 0–10 level
- Simulation duration 2–30 million years
- Simulation speed 0.2–5 million years/s
- Show sedimentary rock layers
- View Internal & external forces, Deformation, Isostasy
- Deformation structure Folds, Reverse fault, Thrust fault and nappe, Normal fault, Horst and graben, Strike-slip fault
- Amount of deformation 0–100 %
- Show labels and stress arrows
- Isostasy situation Mountain range, Ice sheet, Coastal basin
Questions to explore
- With the uplift rate fixed, how does the peak elevation reached change as you increase the external force?
- How does the hanging wall move in a reverse fault and in a normal fault, and which stress makes each?
- Why does the land rise after a thick ice sheet melts?
