Physical Geography Fieldwork
1. Classifying Rocks
Igneous rocks:
 Texture: indicator of how long the molten rock took to cool and where rock was
formed
o Great depths: coarse-textured eg. granite
o Shallow depths: fine-grained but large crystals = porphyritic rocks
o Surface: fine-grained eg. basalt
 Colour: indicator of chemical composition of rocks
o Dark-coloured: low in silica = basic rocks eg. mafic (Magnesium and FerrIC)
igneous rocks
o Light-coloured: rich in silica = acidic rocks eg. felsic (FELdspar and SiliCa) rocks
Sedimentary rocks:
 Clastic: made from rock fragments
o Size of particle they are mostly made up of
 Fine-grained lutites eg. shale
 Medium-grained arenites eg. sandstone
 Coarse-grained rudites eg. conglomerate
 Mix between groups eg. sandstones made from mix of grains
o Proportion of three main grain types: quartz sand, feldspar and lithics
 Eg. sandstone can be split into feldspar-rich arkose sandstones and
lithic sandstones
 Chemical: made from minerals dissolved in water / biochemical: made from
chemicals derived from organisms
o Largest group: carbonates eg. limestones
o Other groups: chalk, coal
Metamorphic rocks:
 Granular: mostly made from single mineral formed by contact metamorphism eg.
marble from calcite
 Foliated: layered texture due to intense compressional pressure formed by regional
metamorphism
o Low-grade eg. slate
o Medium-grade eg. schist
o High-grade eg. gneiss
 Can also classify based on facies (conditions in which particular assemblages of
minerals are formed) / zones eg. Barrovian and Buchan zones in which particular
rocks and minerals are formed
2. Classifying Minerals
The Dana System:
 Chemical composition
o Elements eg. gold
o Compounds eg. lead + sulphur = lead sulphide
 Classify according to anion groups because compounds which have
the same anion tend to be very similar eg. sodium chloride and
potassium chloride – all chlorides tend to form under similar
geological conditions
 Internal crystal structure
o Identifying minerals through X-ray crystallography: identity revealed by how
crystal diffracts rays
o Spectroscopy: testing which colours of light are absorbed
o Looking at the way the crystal polarizes and refracts light
* Write that many mineral classifications today based on Strunz system, but just need to
learn the Dana system
3. Analysis of the Impact of Weathering on Gravestones
 Focus of investigation eg. effect of air quality on rates of weathering
 Constant variables: choose same geology eg. only consider slate
 Fieldwork (the process of getting results)
 Recording and analyzing data: eg. drawing detailed maps to locate precise locations
of headstones, categorise with colour code
 Interpretation and conclusions
* Main thing is the organization of ideas because the rest are dependent on the context
of the question
4. Measuring Soil Creep
 Soil creep: slow downhill movement of regolith that results from constant minor
rearrangements of constituent particles
 T-peg principle
o Draw diagram
o Insert rigid pegs to a shallow depth and resurvey positions of protruding ends
at intervals by reference to some fixed point
o Crosspiece fitted to top of main shaft to accurately measure angular tilt by
spirit level
o Rod inclinometer (device that magnifies necessary angular measurements for
precise reading) fitted over top of peg
o Problems: disturbance by animals / indeterminacy of differential movement
occurring between the rigid stake and deforming soil
 Young Pit method
o Draw diagram
o Dig shallow pit
o Insert grid of horizontal pins a few cm long into a vertical face aligned
downslope
o Positions of ends of pins surveyed with respect to some fixed point and pit is
infilled
o After appropriate interval, hole excavated and positions of pins resurveyed
o Problems: when pit dug out risk of accidental disturbance
o Can connect buried markers with fine wires
5. Measuring Infiltration Capacity
 Ready-made infiltrometer: draw diagram
 Self-constructed infiltrometer: draw diagram
o Tin can strong enough to be driven 30 – 50mm into soil
o Protruding part used as reservoir for water added by student
o Kept topped up to marked depth eg.10mm as contents infiltrate soil, rapidly
initially then more gradually
o Take note of quantities of water added over short time intervals
o Plot mm / min against time interval to get infiltration rate curve
6. Reliability of Forecasting
 Not enough information do describe the state of the atmosphere in detail
o Temperate latitudes more dynamic: small disturbances may be followed by
rapid development and significant changes in state
o Observation stations too widely spaced – cannot detect development areas
which lie amongst them
o Not possible to obtain data from the whole globe for satisfactory forecast for
a few days to be achieved
 Mathematical equations expressing the physical laws too complex for an exact
solution unless simplifications are made
 Extrapolation of past developments to the future may be inaccurate
o Extreme climate change now
o Enormous variety of past weather
o Can only accurately forecast 12h ahead
* There are problems, but forecasting is probably the only option we have
* Problems can be mitigated but never fully resolved