Cameroon GCE O-Level Geology flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Earth's outer core

Liquid iron-nickel layer between the mantle and inner core; its motion generates Earth's magnetic field and it blocks S-waves.

Continental versus oceanic crust

Continental crust is thick, granitic and less dense (~2.7 g/cm³); oceanic crust is thin, basaltic and denser (~3.0 g/cm³), so it subducts.

Igneous rock

Rock formed when magma or lava cools and solidifies. Slow cooling underground gives coarse crystals; fast cooling at the surface gives fine crystals or glass.

Sedimentary rock

Rock formed from weathered fragments or dissolved material deposited, compacted and cemented. Examples are sandstone, shale and limestone, which may contain fossils.

Metamorphic rock

Rock changed by heat and pressure without melting. Examples are slate, schist, gneiss and marble, often showing foliation or recrystallisation.

Mohs hardness scale

Ranking from talc (1) to diamond (10) showing which minerals scratch others. A mineral scratches only minerals of lower number.

Streak test

The colour of a mineral's powder when rubbed on unglazed porcelain. It is more reliable than the mineral's colour, which varies with impurities.

Cleavage versus fracture

Cleavage is breaking along flat planes determined by atomic structure (mica); fracture is irregular breaking with no preferred planes (quartz).

Divergent plate boundary

Where plates move apart, as at mid-ocean ridges. Magma rises, new oceanic crust forms, and shallow earthquakes and basaltic volcanoes occur.

Convergent plate boundary

Where plates move together. Subduction produces trenches, earthquakes, volcanoes and fold mountains; continental collision produces high mountain ranges.

Transform plate boundary

Where plates slide past each other horizontally. Crust is neither created nor destroyed, and earthquakes occur without volcanic activity.

Earthquake focus and epicentre

The focus is the point underground where rupture begins; the epicentre is the surface point directly above it, usually where damage is greatest.

P-waves and S-waves

P-waves are fast compressional waves travelling through solids and liquids. S-waves are slower shear waves that cannot pass through liquids.

Richter versus Mercalli

Magnitude (Richter or moment) measures earthquake energy released; intensity (Mercalli) measures observed shaking and damage at a place.

Shield versus composite volcano

Shield volcanoes have gentle slopes from fluid basaltic lava. Composite volcanoes have steep slopes from alternating viscous lava and ash, with explosive eruptions.

Anticline and syncline

An anticline is an upward-arching fold with the oldest beds in its core; a syncline is a downward-sagging fold with the youngest beds in its core.

Normal fault

A fault formed under tension in which the hanging wall moves down relative to the footwall, often creating a rift valley or fault scarp.

Chemical weathering

Breakdown of rock by chemical reactions such as carbonation of limestone, oxidation of iron minerals, and hydrolysis of feldspar into clay.

River erosion processes

Hydraulic action (water force), abrasion (sediment scouring), attrition (particles wearing each other) and solution (dissolving rock) together cut river channels.

Water table and aquifer

The water table is the upper surface of saturated rock. An aquifer is porous, permeable rock that stores and transmits usable groundwater.

Stalactite and stalagmite

Calcium carbonate deposits in limestone caves. Stalactites hang from the roof; stalagmites grow upward from the floor.

Law of superposition

In undisturbed sedimentary sequences, each layer is older than the one above it and younger than the one below it.

Cross-cutting relationships

A fault, dyke or intrusion is younger than the rocks it cuts through; this principle orders geological events in relative dating.

Index fossil

A fossil of a species that lived over a short time but a wide area, allowing correlation of rock layers of the same age.

Radioactive half-life

The time taken for half the parent atoms in a sample to decay. After n half-lives, (1/2)^n of the parent remains.

Carbon-14 dating

Dating organic remains using carbon-14 decay (half-life about 5,730 years); useful only for material younger than about 50,000 years.

Geological time scale order

Precambrian, then Palaeozoic, Mesozoic and Cenozoic eras. The Mesozoic includes Triassic, Jurassic and Cretaceous periods.

Coal rank sequence

Increasing heat and pressure change peat into lignite, then bituminous coal, then anthracite, the hardest coal with the highest carbon content.

Oil trap

A structure where oil and gas, having migrated from source rock, are held in porous reservoir rock beneath an impermeable cap rock.

Cameroon Volcanic Line

A chain of volcanoes and intrusions running from Atlantic islands through Mount Cameroon to the Adamawa Plateau; Mount Cameroon is still active.

Soil profile horizons

Vertical sequence O (litter), A (humus-rich topsoil), B (subsoil), C (weathered rock) and R (bedrock), showing increasing weathering downward.

Strike and dip

Strike is the compass direction of a horizontal line on a bedding plane; dip is the angle of steepest slope perpendicular to strike.

Map scale 1:50,000

One centimetre on the map represents 50,000 cm, or 500 metres, on the ground; one kilometre on the ground is two centimetres on the map.