Prof. Vic DiVenere
Dept. of
Earth and Environmental Science
C.W. Post Campus - Long Island
University
karst subsidence
soluble rocks: esp. limestone, also dolomite, marble, halite
mixing zone chemistry near top of water table is where most dissolution occurs
structural control (joints & bedding parting) controls location & spacing of caverns
sinkholes: gradual and sudden
stream processes
- hydrologic cycle
- stream gaging,
stream discharge: Q = VA,
hydraulic radius
- stream velocity profile - slowest along bed and banks (friction)
- drainage networks, stream orders, drainage divides
- groundwater-surface water relationship
gaining streams (baseflow) and losing streams - stream loads: bed (sand and gravel), suspended (silt and clay), dissolved (ions in solution)
- stream hydrographs and precipitation events
- baseflow
- stream loads: bed load, suspended load, dissolved load
- stream competence and capacity
- stream velocity vs. transport and erosion: Hjulstrom's curve
- floods and stream erosion/deposition
- flood recurrence interval: T = N+1 / M
- large flood frequency, "100 year floods"
- floodplains, natural levees, flood deposits
- artificial levees and effect on flood frequency and magnitude
- artificial deepening and widening of streams to control floods
- influence of bedrock, land use, and development on frequency and degree of flooding, flash flooding
- meandering streams: point bars, cut banks
competence and capacity on inner and outer banks of a bend in a river
- stream valley evolution: youth (steep sided, V-shaped), mature (gentler slopes, flood plains)- youthful and mature stream valleys (profiles)
- graded streams (concave up profile b/c of increasing discharge downstream & increasing flow efficiency)
-
effect of dams and sea level change on the graded profile
- the influence of dams on a graded stream
delta grows out into reservoir, aggrades upstream
stream erosion downstream of dam b/c seds deposited behind dam
coastal processes
waves
- size of waves determined by wind speed, duration, and fetch
- gravity waves and capillary waves
- crest, trough, wavelength (L), wave heigth, period
- celerity (wave speed)
- orbital motion of water as wave passes, decreases to zero at depth of L/2
- what happens to a wave as it approaches shore (when water depth < L/2)
- breakers, swash, backwash
- beach profile: shoreface, berm, dune
- rip current
- coastal sedimentation: coarse in the shoreface, progressively finer going offshore
- littoral drift (longshore drift)
- sand spits & hooks
- wave refraction
- winter/summer profiles, beach scarps (caused by storm waves w/ littoral drift)
tides
- equilibrium theory of tides: gravitational and centrifugal bulges from moon and sun
- phases of the moon and tidal range (high to low)
- neap and spring tide
- problems with equilib. theory: seafloor drag and continents in way
- dynamic theory of tides: tidal bulges rotate [ccw in N Hem, cw in S Hem] around a point (2x/24 hr)
- tides and barrier islands: tidal currents and maintenance of lagoons and inlets
sea level rise
- present 2 mm/yr sea level rise, ~ 1 foot rise in 20th century
-
gently sloping East and Gulf Coast shorelines receding rapidly > 1 ft/yr
- sea level should rise another 2 ft to significantly more in 21st century
barrier islands
- foreshore, berm, dunes, +/- forest, marsh, lagoon, marsh, mainland
- form on gently sloping coastal plain type shorelines
- migrate landward with rising sea level
storm surge and coastal erosion
- inverted barometer effect: low pressure ("noreasters" and hurricanes)
- wind setup: onshore storm winds pile up water against the shore (storm surge)
return flow of water along thee seafloor carries additional sediment offshore (erosion)
- tides, storms, and coastal erosion and flooding
wind setup + high tide (esp. spring tide) = worst erosion & flooding
- storms may cause short term retreat of the shoreline but eventually, the shoreline build back
out to longterm shoreline trend (typically slowly receding due to sea level rise)
protecting the shoreline?
- effects and effectiveness of groins, seawalls, and beach nourishment
- dune stabilization as a coastal protection method is only temporary
when extreme storm waves overtop the dunes they deposit sediment on back side of barrier island
in this way the barrier island can migrate landward with rising sea level
when dunes are stabilized the barrier island simply gets narrower and waves ultimately erode away the dunes
seismology and earthquake hazards
- plate boundaries and earthquakes
- gradual stress buildup -> stress exceeds strength of rocks -> sudden motion on fault
- body waves (P & S waves)
- surface waves (Rayleigh and Love waves)
- principle of the seismometer
- accelerometer
- S-P interval gives distance to earthquake
- triangulation: S-P interval recorded by at least 3 seismic stations allows location of earthquake
- epicenter and focus (hypocenter)
- first motion studies to determine the type of fault that moved in an earthquake
- using S-P interval and maximum amplitude to determine Richter Magnitude
- magnitude scale = logarithmic scale of ground motion
- moment magnitude scale of energy released in an earthquake
- number of earthquakes of various magnitudes per year (qualitative)
- energy release in small vs. large earthquakes
- Mercalli intensity scale
- quantitative relationship between the intensity and magnitude scales
- earthquake prediction? - possible precursors (see pages 470-471)
- earthquake risk estimation (e.g., figures 11.24 - 11.27)
- seismic gaps as areas of increased risk in the near term
- case studies:
San Francisco, 1906 - fires did most of the damage
Loma Prieta, Ca., 1989 - damage dependent on the stubstrate (bedrock vs. bay muds vs. fill)
Parkfield, Ca., 2004 - even when you think you can predict one, it fools you
Alaska, 1964 - a great earthquake, big tsunami, seismic gaps remain
Mexico City 1985 - damage to specific size buildings, tuned to the thick lake bed sediments
Ismet, Turkey, 1999 - an ominous westward sequence toward Istanbul
New Madrid, Mo, 1811-1812, 3 great earthquakes > 8.0, on an inactive? ancient fault
felt much farther away than west coast earthquakes (sedimentary strata)
NYC - could a damaging earthquake happen???