types
sea rivers groundwater weathering geohazards and landslides earthquakes two cause hypotheses of earthquakes
sea
- wave erosiona and brushing on rocks wears at lower strata creating cliffs.
- conglomerates usually give away to these waves
- waves are produced by frictional drag of wind
- in HK pearl river, seawater goes from E-W
rivers
-common chinese rivers: Yangzte, xiao-jiang catchment basin
groundwater
results from permeable rock giving water from pressure of some kind
pervious
permeable
unconfined aquifers
- groundwater only partially fills aquifer
- levels follow contour of land and bodied water
- can be contaminated from surface activity
confined aquifers
- aka artesian aquifers
- sandwiched between 2 confining beds creating pressure
- water level in well when drilled is the pressure surface
weathering
- mechanical disintegration
- chemical decomposition
mechanical weathering or disintegration
- caused by physical processes such as frost, permeating water, and temp/stress changes
- results in opening/new discontinuities, rock/mineral grain fracture
- another common in hk, Tree root expansion/growth
chemical weathering or decomposition
- chem rxtions change rocks into new rocks
- hydration, oxidation, ion exchange/solution
- silicate minerals>clay minerals
- quartz survives
- carbonate rocks
grades of chem decomposition
- slightly Decomposed: stained near joints
- moderately “: easily broken by geo hammer and is completely stained
- highly “:broken by hand
- completely “: is soil but still has original rock texture
- residual soil: is soil with no rock texture
Mechanical strength of weathered granite
-grades 1-4, 1 is unweathered
mass weathering
- largely controlled by joint characteristics
- plutonic rocks is of importance to geo eng
Mechanical strength of tuff
- grades 1-4, 1 and 2 are extremely strong
- stronger and more abrasive than granite
corestone
A rounded or broadly rectangular joint block of granite formed as a result of subsurface.
weathering of carbonate rocks
- calcite dissolves with h2o
- mechanical weathering can happen too
classification of rock mass weathering
-PW90/100: rock occupies 90 to 100% and soil occupies 10 to 0%of exposed area, similar numbering for rest of situations
products of rock weathering
- original minerals form in-situ soils
- new clay minerals form “
- solutions flow away from chem
geohazards
- events caused by geo features and the processes that make them
ex: sinkhole in Guatemala, ground caving (subsidence) in Venice, - landslides are biggest concern in HK
Earthquakes
- releases large amount of energy in short time
- generates seismic waves in crust
- includes focal depth, focus (point of initial rupture, aka hypocenter), epicenter (point on surface above focus)
- mag>8 on richter scale is usually catastrophic
Seismic waves
- primary wave (P-wave): compression/dilation wave (slinky)
- secondary wave (s-wave), like a string
- love wave: particles are bunched at peak
- Rayleigh Wave: particles are bunched at trough
seismograph
- records earthquakes
- richter scale: M_r=log(A) where the A is the averaged 2 max amplitudes given by wood-anderson type seismograph
Two cause Hypothesis of Earthquakes
- elastic rebounding: earthquake energy comes from elastic stress-strain energy in rocks; ex) san andreas fault California
- reids’s theory: fence example
- Deep-Fault-natural gas: Earthquake energy= volumetric Expansion energy of nat gas: ex) wenchuan , lengmen shan, sichuan province
