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Rock deformation and geological structures

5 dot points across 5 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do you measure the orientation of a bed and work out its true thickness?

Dip, strike and true thickness: the definition and measurement of true dip, apparent dip, dip direction and strike with a compass-clinometer; structure contours; the calculation of the true (perpendicular) and vertical thickness of a bed from its outcrop width and dip using trigonometry; the distinction between vertical and true thickness; and the rule of Vs for outcrops crossing valleys.
A focused answer to the Eduqas Geology statement on structural measurement. Covers true dip, apparent dip, dip direction and strike, measuring with a compass-clinometer, structure contours, the calculation of true and vertical thickness from outcrop width and dip using trigonometry, and the rule of Vs, with worked KaTeX calculations for Components 1 and 3.
14 min answer →

How do you recognise and classify folds, faults and joints, and read them on maps?

Folds, faults and joints: fold elements (limb, axial plane, hinge) and types (anticline and syncline, symmetric, asymmetric, overturned, recumbent, monocline); fault types and the stress they record (normal from tension, reverse and thrust from compression, strike-slip and tear from shear); dip-slip versus strike-slip movement; throw, heave and the fault plane; joints as fractures with no displacement; and reading these structures on geological maps and cross-sections.
A focused answer to the Eduqas Geology statement on folds, faults and joints. Covers fold elements and types (anticline, syncline, symmetric, asymmetric, overturned, recumbent, monocline), fault classification and the stress each records, throw and heave, joints as undisplaced fractures, and how to read these structures on maps and cross-sections for Components 1 and 3.
14 min answer →

How do you read a geological map and turn it into a cross-section and a sequence of events?

Geological maps and cross-sections: reading outcrop patterns, reading dip from outcrop width and topography, and the younging direction; constructing a cross-section from a map; deducing the geological history (the order of events) using superposition, cross-cutting relationships, unconformities and included fragments; the difference between simplified map extracts (Component 1) and real published map extracts (Component 3); and three-point problems in outline.
A focused answer to the Eduqas Geology statement on geological maps. Covers reading outcrop patterns and dip, the younging direction, constructing a cross-section, deducing the order of events with superposition, cross-cutting, unconformities and included fragments, simplified versus real map extracts (Components 1 and 3), and three-point problems in outline.
14 min answer →

What controls whether a rock bends, flows or snaps when it is stressed?

Stress and strain: the three stress regimes (compression, tension and shear) and the strain (deformation) they produce; elastic, ductile and brittle behaviour; the factors that control deformation style (temperature, confining pressure, strain rate, rock type and pore fluid pressure); competent and incompetent rocks; and why rocks deform ductilely at depth but brittlely near the surface.
A focused answer to the Eduqas Geology statement on rock deformation. Covers compression, tension and shear stress and the strain they cause, elastic, ductile and brittle behaviour, the controls on deformation style (temperature, confining pressure, strain rate, rock type, pore fluids), competent versus incompetent rocks, and why rocks behave ductilely at depth and brittlely near the surface.
13 min answer →

What does an unconformity tell you about the missing chapters of Earth history?

Unconformities and the geological record: the angular unconformity (tilted or folded beds overlain at a different angle), the disconformity (parallel beds separated by an erosion surface) and the nonconformity (sediments on eroded igneous or metamorphic basement); the ordered sequence of events each records (deposition, uplift, tilting, erosion, renewed deposition); the gap (hiatus) in the record; and the use of unconformities to reconstruct geological history on maps and cross-sections.
A focused answer to the Eduqas Geology statement on unconformities. Covers the three types (angular unconformity, disconformity, nonconformity), the ordered sequence of events each records, the gap or hiatus in the geological record, and how unconformities are used to reconstruct geological history on maps and cross-sections for Components 1 and 3.
13 min answer →