Geological Structures and Karst Sandbox · KarstLab

A strata sandbox you can cut open. In the west, see an anticline, a syncline and an east-dipping normal fault, and understand why anticlines become valleys and synclines become ridges. In the east, see tower karst and dolines, then follow a stream through a sinkhole into an underground river and cave. Move the cross-section, click any landform for notes, then finish the guided tasks and quiz.

Subject: Geography · Level: High school · Topics: Anticlines and synclines, Topographic inversion, Normal faults, Karst landforms

Chapters

Folds: anticlines and synclines

Compression has bent the western beds into folds. An upward arch is an anticline; a downward bend is a syncline. Find each one on the sandbox.

Read the age of the rock

To identify a fold, compare rock ages: an anticline is older at the centre and younger on the limbs; a syncline is younger at the centre and older on the limbs. Move the cross-section, click both cores and check the legend.

Topographic inversion

You might expect an arched anticline to be a mountain, yet here it is a valley; a sagging syncline should be a valley, yet here it is a ridge. This is anticlines becoming valleys and synclines becoming ridges: the fractured crest erodes easily, while the dense trough resists.

Fault

When stressed rock breaks and clearly slips along the break, it forms a fault. This fault plane dips east and the eastern hanging wall has moved down, making it a normal fault. See on the cross-section how the same bed is offset.

Surface karst

The east is thick limestone. Water containing carbon dioxide keeps dissolving it, leaving groups of tower karst and sunken solution dolines.

Water goes underground

Follow the stream to the sinkhole. The water drops down the shaft into the underground river, crosses the cave and leaves through the east wall. Move the cross-section near the passage and look inside.

Cave deposits

Dissolution makes the cave; deposition decorates it. Calcium bicarbonate in the water breaks down and calcium carbonate precipitates. Stalactites grow down from the roof, stalagmites grow up from the floor, and together they join into columns.

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