C -> 2.6-2.9 Flashcards
abrasion
this is the force of the bits of rock carries in the water blasting into the rock
hydraulic action
force of water hitting the cliff and squeezing air into the cracks in the rock
attrition
this is the process of rocks hitting each other and breaking into smaller rocks
corrosion
chemical reaction between sea water and minerals in the rock
moeraki boulders, Koekohe beach, new zealand
- mudstone Concretions - lumps of sediment bound together by a calcite cement, formation began over 60 million years ago. Exhumed of mudstone by coastal erosion, after this marine mud began to form in it, and then coastal erosion meant that the bedrock and mudstone enclosing them got smoked, leaving it exposed.
Lithology
general physical characteristics of a rock or rocks in a particular area
Lithology, wave type + size are significant factors in determining rate of erosion
Highcliffe/ Barton
- Christchurch bay, solent coat
- concordant coast: barton sands lie onto of barton clay
- 25-35m high vliffs
- average erosion rat on 1m/year
- testbed for lots of engineering geology experiments, eg, groins/ revetments/ boulder
why stresses/strengths may be more complicated
- rock might be sedimentary/ unconsolidated materials
- there are multiple causes of change - hard to manage
- failure is often deep in the cliff, so lots of material is moved
prolonged rainfall
will saturate soil and encourage soil movement
buildings
increase weight on slope and add to downward pull of gravity
removal of vegetation
roots bind up soil and vegetation absorbs some of the moisture
excavation
undercutting of slope increases instability
permeability
water flowing on surface of impermeable layers
rock type
weak saturated material or shattered rock is more likely to move than solid bedrock
bedrock
solid bedrock below weak material: the junction forms the likely slide plane
jurassic coast
- number of different mass movements events here since 2000 (including major landslip 300m long in Lyme Regis, 2008)
- combination of wet weather, Marine processes and geological relationship (sandstone on clay) makes the cliffs very unstable along this coast
mudflows
often occur when water is channelled locally to saturate the soil - thus creating rills (eroded gully) and lobes (front edge of deposition)
talus slopes
larger boulders at core with smaller material on top - often it at 34-40o angle of rest depending on size of fragments (larger = steeper due to friction between rocks)
rotational slumps
vegetation layer often remains intact to create distinctive terraces with bare scar faces between - like a series of steps
block slides
debris material tends to stay in larger sizes - often leaves a clean scar above along the failure line, eg bedding plane
Vegetation role in stabilising
stabilise unconsolidated sediment and protect it from erosion as plant roots bind sediment together and stems and leaves interrupt flow of water and wind, encouraging deposition.
Pioneer plants role
- Pioneer plants stabilise sediment, add organic matter which retains moisture, contributes nutrients and provides shade + reduces evaporation in sand.
Xerophytic plants specially adapted
to dry conditions to colonise bare sands plant succession on sand called psammosere
Psammosere 1-3
- Embryo dunes form when seaweed driftwood or litter provides a barrier to trap sand
- As embryo grows, colonised by xerophytic pioneer plants like saltwort, embryo dunes alter the conditions to something other plants can tolerate - allowing other plants to colonise and forms a foredune
- Pioneer plants stabilise the sand, allowing marram grass to colonise
Psammosere 4-6
- Marram grass has waxy leaves to limit transpiration loss, 3m roots to reach down water table, allows dune to grow rapidly forming a yellow dune
- As marram grass dies, adds hummus to sand, creating soil, which develops a grey dune.
- Soil now above high tide level, so rain washes salt from soil making it less saline
End stage of psammosere
Soil now has improved nutrients and moisture retention, so normal planters can colonise until climax plant community reached
Halophytic plants specially adapted for
saline conditions, estuarine areas are ideal for salt marshes because they’re sheltered from strong waves, river transport a supply of sediment to the river mouth, which may be added to by sediment flowing into the estuary at high tide
Halosere A-C:
A. Mixing of fresh and sea water in estuary causes clay particles to stick together and sink - called flocculation
B. Blue green algae and gut weed colonise mud, exposed at low tide for only a few hours
C. Algae binds mud, adds organic matter and traps sediment
Halosere D-F:
D. As sediment thickens, water depth is reduced and mud covered by tide for less time
E. Halophytic glasswort and cord grass colonise as the next serial stage, marsh is still low and covered by spring tides
F. An accumulation of organic matter and sediment raises height of marsh until only covered by spring tides
Final stage halosere:
Higher marsh colonised by less hardy plants, rainwater then washes salt out of high marsh’s soil, allowing land plants to colonise, which continues until climax community reached
Oregon USA sand dunes
Oregon, USA - 40 miles along pacific coast, largest coastal sand dunes in NA, 2.5 miles inland. Banshee hill dune reaches 500ft high and popular are for ATV
Mass movement is
downslope movement of material under the force of gravity, umbrella term for a wide range of specific movements including landslides rotational slumping and block fall. When gravitational force exceeds resisting forces of friction and internal rock cohesion
Type of mass movement depends on
lithology, unconsolidated material = slumping,
consolidated rock - sliding.
Blockfall
on slopes with more than 40o, where rock fragment breaks away falls down slope, initiated by mechanical weathering to marine erosion (H,A, undercutting creating wave cut notch). Cliffs prone to blockfall have a geological structure with many hints, faults or bedding plants + steep. April 2013, large blockfall in st Ostwalds bay on south Dorset, 80m section chalk cliff.
Landslides
downsloping movement of discrete blocks of rock down a flat plane, when weathering loosens blocks, and gravity brings it down.
Giants causeway is an
Emerging coastline, as high tide doesn’t reach the grass, so there is rock succession and it is not an actively receding coastline
