Weathering And Soils

Front 1

What is soil?

Back 1

Mixture of weathered mineral debris and plant material (<1m) top soil = plant rich, sub-soil = clay-rich

Front 2

What is weathering?

Back 2

Natural decay and breakdown of rock, or drift, that is in contact with air and water; generally depth of <10m

Front 3

What is drift?

Back 3

Transported, superficial sediment deposited on top of the bedrock; mostly unconsolidated clay, sand and coarser clastic debris

Front 4

What is colluvium?

Back 4

Slope debris, moved downslope largely by gravity alone; so relative extent of sediment transport drift>colluvium>soil; includes debris from creep and sheetwash, also head and scree. Increases with loss of vegetation

Front 5

What is rockhead?

Back 5

The buried drift/rock interface ; commonly a conspicuous boundary between weak soils and drift and the underlying strong rock; may be less well defined in deep profile of weathered rock ; formed as erosion surface before drift deposition so it's topography may be totally unrelated to modern surface

Hint 5

Front 6

Define engineering soil

Back 6

Weak material that can be excavated without ripping or blasting, therefore including soil, drift, weak rocks and weathered rocks

Front 7

Describe 6 physical weathering processes

Back 7

Unloading joints: stress relief fractures, due to over-burden material removal

Thermal expansion: fracturing, due to daily temperature changes

Frost shatter: fracturing, as fissure water or porewater freezes and expands.

Wetting and drying: movement, due to loss or gain of water in clays

Root action: tree root expansion in fissures, and rootlet growth in pores.

Crystallisation: growth of salt crystals, where groundwater evaporates

Front 8

Describe 4 chemical weathering processes

Back 8

Solution: mainly of calcite and gypsum, in sandstone cement, veins and limestone.

Leaching: selective removal of solutes or specific elements

Oxidation: notably rusting and breakdown of iron

Hydrolosis: most silicates react with water to form clay minerals

Front 9

Weathering profiles in rock

Back 9

Front 10

Describe pinnacled rockheads in the weathering of limestone

Back 10

Have deep fissures, mostly filled with soil, between weathered limestone pinnacles, all beneath soil or drift cover (creates difficult foundation conditions prone to sinkhole subsidence)

Front 11

What is a karst?

Back 11

A landscape, normally on limestone, characterised by underground drainage, caves, sinkholes, dry valleys, this soils and bare rock outcrops

Front 12

Describe fluvial processes

Back 12

the action of rivers and flowing water - dominant in all climate regions except arid and permanently frozen regions