Feature Mapping Flashcards
what is feature mapping
set a techniques used to represent various features of the landscape on plain view (map)
why use feature mapping
help map positions of geological boundaries
aspects to identify when doing feature mapping
-bedrock at surface
-lineaments
-breaks in slope
-sinkholes and spring lines
-soil and vegetation
-manmade features
what are bedrock
-hard, solid rock beneath surface materials such as soil and gravel
- also underlies sand and other sediments on ocean floor
-bedrock is consolidated rock, solid and tightly bound
-overlying material is often unconsolidated rock, made up of loose particles.
what are outcrops
-exposed bedrocks
-can be seen on some mountaintops, along rocky coastlines, in stone quarries, and on plateaus
-exposed through natural processes such as erosion or tectonic uplift
importance of bedrocks
determining depth and type of bedrock helps describe the natural history of a region, identifying rock formations
rockhead
top surface of the bedrock
bedrock at surface
used to describe parts of landscape where rockhead is within 1m of land surface
includes areas where bedrock is overlain only by soil and vegetation, and by thin (and typically patchy) superficial deposits that are less than 1m thick, as well as those areas where the bedrock is actually exposed.
areas where bedrock is not at surface usually appear much more ‘rounded’, smoother and less ‘regular’ than areas where bedrock is at surface
bedrock at surface in upland terrains
areas where bedrock is at surface:
-dominated by exposures,
-by immature or poorly developed vegetation
-by jagged topography
areas where bedrock is not at surface:
-flat
-highly vegetated
-are typically limited in lateral extent
bedrock at surface in lowlands terrains
areas where bedrock is at surface:
-sporadic outcrops
-show ridges, gullies and bumps in the landscape between those outcrops
areas where bedrock is not at surface:
-mounded or irregular lumps and bumps that are without clear trend
flat ground
limits to bedrock symbols
dotted black ink line
what are lineaments
linear feature in a landscape which are an expression of the underlying geological structures such as a fault
lineaments symbol
blue line dot alternations
what are breaks in slope
-point in hillside where the gradient (slope angle) changes
-basic idea is that rocks of different competencies will weather differently and produce hills slopes of different angles
-if breaks in slope can be mapped, and they can be related in some way to the underlying rocks, then they can be used to interpret the position of geological boundaries through areas of poorly exposed ground
what is a boundary
also known as margin/plate boundary, point where two plates meet
breaks in slope for bedrock geology
In most instances, geological boundaries will not coincide with breaks, but they will have some relationship to them
breaks in slope for faults in uplands and lowlands
uplands:
lineaments rather than breaks in slope
lowlands:
subdued pattern to the breaks in slope. Clear offsets in breaks, or offsets in patterns of breaks
what are springs
where the water table intersects the surface
places where groundwater flows naturally from the aquifer onto the land surface or a body of surface water
Almost all streams and rivers have springs or seepages as their ultimate source, or are fed by them at various points along their courses
how is a spring formed and founded
result of an aquifer being filled to the point that the water overflows onto the land surface
or forced to the surface when there is a relative difference in permeability of rocks (flow from more permeable to less permeable)
what is an aquifer
body of permeable rock which contains or transmits groundwater
e.g gravel, sandstone, conglomerates, and fractured limestone
what is the water table
underground boundary between water-saturated ground and unsaturated ground
underground boundary between the soil surface and the aquifer
what is ground water
water found in the aquifer
what is a sink hole and how are they formed
depressions in the ground that forms when water dissolves the surface rock
streams may flow and disappear underground
where are they typically found
occur only where the underlying geology is limestone
where the underlying geology changes from clastic sedimentary or igneous strata above, to carbonate strata below
why interpret soil and vegetation in feature mapping
direct reflation of underlying geology
Vegetation strongly dependent on the mineral/moisture content of soil
types of vegetation can be linked directly to specific bedrock lithologies.
degree to which soil holds water related to the permeability of the bedrock beneath it.
what areas do you use soil and vegetation interpretation
areas not covered in superficial deposits
not been heavily cultivated
what are superficial deposits
youngest geological deposits
formed during the Quaternary period
short green grass indicates
soil well drained and developed
long grass and reeds
poorly drained soils
heather and short patch grass
well drained but poorly developed soils
