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geomorph exam 1
geomorphology terms and information for exam 1
| Question | Answer |
|---|---|
| geomorphology | study of landscapes and the processes that shape them; 1880s, knowledge of erosion; bridge between geography and geology |
| goals of geomorphology | classify landscapes and associate landforms with processes |
| historical geomorphology | evolutionary development of landscapes under a wide variety of climatic and geologic controls |
| process geomorphology | study of earth surface mechanics and how processes lead to the creation and subsequent modification of landforms |
| process | action when an applied force results in either chemical or physical changes |
| endogenic geomorphology | processes from earths interior associated with tectonics and volcanoes |
| eight exogenic categories | soil/hillslope, fluvial, aeolian, glacial, periglacial, coastal, karst, biogeomorphology |
| steno | superposition; graph of cave falling in to explain folds |
| hints of geomorphology | herodotus and socrates postulated about the nile river delta |
| uniforitarianism | james hutton, processes happening now have operated over long geologic timescales |
| catastrophism | baron cuvier, large changes are from catastrophic events, biblical |
| louis agassiz | studied glacial debris; decided there were more glaciers across NA than originally thought |
| john wesley powell | introduced concept of base level, traveled grand canyon |
| base level | sea level; elevation at which the land surface can no longer be eroded |
| grove karl gilbert | first process geomorphologist, how erosion and transport create and modify landforms; defined open system |
| william morris davis | geographic cycle; expanded on sea level; structure, process, and time; defined closed system |
| geographic cycle | old age, uplift, youth (valleys, low-relief uplands), maturity, high relief steep slopes, erosion, late maturity |
| j harlen bretz | studied the channeled scablands, wallula gap, jokulhlaps, deep and high velocity floods created ripples |
| equilibrium | ability of an open system to self-regulate and stabilize through negative feedback mechanisms |
| dynamic equilibrium | landscape adjusts to processes; cause-effect; ROC declines with time |
| closed system | no addition of subtraction of energy or matter; clearly defined boundaries; function of time |
| open system | movement of energy and matter; steady state, not dependent on initial conditions; self regulation is not time dependent |
| static equilibrium | conditions remain same for span of days to months; things are not changing in such a small time frame |
| steady state equilibrium | conditions fluctuate around average conditions for decades to thousands of years |
| steady time v. graded v. cyclic | steady: straight flat line graded: wave cyclic: curve made up of waves |
| force | anything that changes state of motion in a body |
| stress | force acting per unit area |
| driving forces | stresses on earths surface |
| what causes resistance on earths surface | lithology and structure |
| hydrologic cycle relevance | movement of water, climate, proximity to water |
| gravity relevance | fluid movement downslope, mass wasting, tides, isostasy, geoid |
| internal heat | radioactive decay; plate tectonics |
| cuestas | gently dipping resistant sandstone layered with weaker materials, weak material eroded, leaves behind a scarp |
| 5 principles of geomorphology | 1. equilibrium 2. force v. resistance 3. changes occur when a threshold is exceeded 4. process linkage 5. analyse over variety of timescales |
| threshold | critical conditions at which a geomorphic system can be destabilized and enter disequilibrium |
| extrinsic threshold | changes in driving forces results in readjustment of system |
| intrinsic threshold | subtle progressive reduction of landform resistance results in readjustment |
| fluvial equilibrium | rivers tend towards an average condition even with expected disturbances in flow and sediment loads |
| reaction time | length of time between initial disturbance and initial reaction of fluvial system |
| relaxation time | length of time the system takes to make adjustments following disturbances |
| response time | sum of reaction and relaxation time; length of time from onset of disturbance to the persistence of new equilibrium conditions |
| recovery time | time to reacquire former equilibrium conditions |
| complex response | all processes and system components dont reach threshold conditions at the same time |
| process linkage examples | volcano to melting ice to lahar to downstream aggradation to frequent flooding |
| positive feedback | process that reinforces the tendency of a system to change its condition following a distrubance |
| what is channel geometry controlled by | average streamflow and sediment load |
| what are the 6 controls on geomorpology | gravity, climate, geology, biology, anthropogenic land use, anthropogenic controls |
| what is the big picture of endogenic and climatic geomorphology | external controls resulting in generation or obliteration of surface relief; processes not always oppositional |
| oblate spheroid | distance to earths center from pole is 1/300th shorter than to the equator; pressure gradient results in spherical shape, centrifugal force |
| mantle mobility | ability to achieve hydrostatic equilibrium |
| negative feedback | step back to correct what happened/took the system out of equilibrium |
| geoid | reference surface of gravitational equipotential, coincides with sea level, differs as a result of unequal mass distribution in the crust and mantle |
| hypsometric curve | proportions of earth surface elevations above and below present sea level; bimodal distribution of elevations; represents difference in rock density and continental erosion |
| how do elevation and continent size relate | big continent = high elevation |
| orogenic processes | mountain building, fold and thrust belts, crush |
| epeirogenic processes | regional uplift or depression that does not disrupt original structures; mantle plumes; isostasy; simple uplift |
| isostasy | depth of compensation beneath a defined surface; pressure of overlying rock will be equal regardless of rock column height above this level |
| continental freeboard | mean elevation of continental mass above sea level |
| exhumation | surface erosion revealing buried rock |
| steps of isostatic equilibrium | subsidence and uplift occur simultaneously, uplift is a negative isostatic anomaly while subsidence is a positive |
| steps of isostatic mountain peaks | low relief surface is uplifted above base level, rivers incise, isostatic compensation uplifts |
| flexure | downwarping and upwarping of the lithosphere in response to a load during short timescales |
| forebulge | lithospheric uplift due to any topographic load |
| fluvial terraces | offshore sedimentation; uplift of nearby land surface |
| foreland basins | depressional margin of compressional fold and thrust belts |
| what tectonic forcing did davis think? | impulsive |
| what tectonic forcing did penck think? | varying |
| which tectonic forcing did hack think? | sustained |
| how does plate tectonics control endogenic processes | boundaries create different landforms and have different processes; marine and continental settings differ |
| island arc | subduction of oceanic plate beneath another |
| cordilleran | subduction of oceanic plate beneath a continent |
| collisional | collision of two continental plates; thrust faulting |
| extensional | complex normal and strike slip faulting, rift valleys |
| coastal geomorphic markers | tectonic or eustatic induced sea level rise and fall |
| marine and inland strath terraces | sea level rise = tectonic uplift rate; waves cut a platform |
| tectonically inactive mountain structure | apparent as alternating ridges of resistant rock and valleys of weak rock |
| joints | parallel fractures, equal distant apart; ductile folding causes brittle fracturing; preferred weathering and erosion along joint planes |
| define rift valleys | large scale extension from thermal uplift |
| horst | uplifted fault block produced by movements along normal faults |
| graben | down dropped block produced by movements along normal faults |
| common features along active mountain escarpments | triangular facet and v shaped notches |
| fault scarp | direct offset of land surface by fault movement |
| faultline scarp | associated with differential erosion along fault line |
| releasing bend | makes basins |
| restraining bend | makes shallow hills |
| paleoseismicity | determined by trench studies; usually oriented normal to fault plane; examination of buried soils associated with individual rupture events |
| neotectonics | use surface features to infer subsurface movements; quarternary |
| 3 main volcanic landforms | lava plains, cones, calderas |
| lava plains | low viscosity; basaltic; effusive |
| lava capped ridges | associated with resistant extrusive igneous rock and differential weathering |
| shield volcanoes | basaltic flows, very large; creates large, shield shaped cones; mauna loa |
| stratovolcanoes | accumulation of both pyroclastic deposits and lava flows; steeper slopes; thicker lava |
| cinder cones | tephra dominated; lava flow occurs in final stage when viscous lava plugs vent; loose pyroclastic material with some lava flows; very steep |
| calderas | depression larger than crater; caused by collapse of magma chamber; associated with extensive ignimbrite sheets |
| inselberg | weathered surface expression of exhumed intrusive igneous rock; preferential weathering along fractures |
| climatic geomorphology | study of how landforms develop in different climates; geomorphic mechanics vary by type and rate depending on temperature and precipitation regimes |
| problems with climatic geomorphology | lithology, tectonic forcing, relict landforms |
| milankovitch cycles | variations in solar radiation |
| eccentricity | 100,000 year cycles; distance from sun |
| obliquity | 41,000 year cycles; variations in earth's axial tilt |
| precession | 22,000 year cycles; variation in earth's axial orientation |
| climate oscillations vary according to: | timeframe, location, intensity |
| eustatic sea level change | global sea level rise or fall commonly induced by glacial/interglacial cycles; results in considerable geomorphic response |
| why were there frequent changes in the quaternary sea level? | multiple episodes of fluvial incision and aggradation (cut and fill sequences) |
| sediment yield | associated with climate; peaks for semiarid continental zones, moist mediterranean zones and monsoon dominated zones; seasonally important |
| interior north america sediment yield | first peak: continental semiarid second peak: humid mediterranean third peak: monsoon |
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