GEOL 315 QUIZ 3
List the 5 factors governing landscape evolution?
1. Tectonics 2. Climate 3. Topography 4. Geology 5. Biology
List three reasons why rivers leave behind terraces.
1.changes is sediment supply 2.tectonic 3. Change in climate
What are the three primary Milankovitch cycles and together how are they thought to control climate change over time?
Eccentricity, obliquity, precession of the equinoxes together these three form Milankovitch cycles which are contributing factors that controls earth's climate
What is the relationship in ice cores between the concentration of CO2 and paleotemperature?
Ice cores indicate as Co2 increases over geological time temperature has also increased
Define longshore drift and explain why it is important for coastal geomorphology.
Longshore drift: moves large amounts of sediment along beaches due to a fundamental asymmetry of sediment transport by wind-driven waves and gravity Produce net transport along coastline Important: material delivered to coastal environments moves parallel to shore Nourishes beaches until transported offshore to deeper marine environments
Worldwide, how do chemical and mechanical denudation rates compare?
Poles- all/only mechanical weathering, chemical fluxes will be zero Equator- intense chemical weathering, chemical fluxes will be high Have to consider gradient- Rates of chemical and mechanical denudation tend to be related. The higher altitude the greater the denudation rates In a global scale the
Describe the history of sea level globally over the past 21,000 years.
21000 y/a: global average sea level stood about 130m below present level 21,000- 7,000 y/a: rising sea level 1cm/ yr 7000-5000 y/a: slowed to less than 2mm/yr 3000 y/a: global sea level began to stabilize Today rising 2mm/yr because of global warming/climate change /ocean warming
Compare and contract diffusive and advective sediment transport.
According to mathematical modeling both diffusive and advective sediment transport produce "realistic-looking" landscapes. Diffusive sediment transport- slope dependent transport, becausec rate of transport depends on gradient - produce convex rounded hillslopes. Advective sediment transport- dominate large drainage areas, produce concave valley systems
Contrast shoreline geomorphology at active and passive continental margins
Active: coastal mountain range hosting volcanoes ,narrow continental shelf, that drops to a deep submarine trench Passive:coastal plain, part of which was continental shelf during higher wide continental shelf, low-relief depositional coast, have a wide piedmont and relatively subdued topography
Sketch a river longitudinal profile and explain (giving three reasons) why the slope of the longitudinal profile changes in the downstream direction.
The rate of stream power loss is uniform along the length of the channel, generally no flood plains in upland streams, grain size is small.
Explain why many of our planet's major surface features correspond to current or ancient boundaries between tectonic plates (page 397)
The regional tectonic settings of active plate margin, passive continental margin, continental interior strongly influence landforms via tectonic deformation and uplift, difference in rock type, and changes in the degree of fracturing . Distinct topography characterizes plate margins with different types of lithosphere (oceanic and continental)
Explain how and why the sediment delivery ratio changes as a function of basin scale and integration time.
The sediment delivery ratio increases with the timescale over which it is integrated and decreases with increasing basin area. The sediment delivery ratio differs by on the amount of time, process its delivered by, and the forces exerted. Only a certain amount can be delivered at one time not to overflow the basin.
Predict the response of climate if rock weathering rates increase.
Weathering of silicate rocks can reduce drawdown of atmospheric CO2 this has reduce greenhouse effect during mezo and ceno era.
When and where does coastal subsidence happen?
When: accompanies large subduction-related earthquakes along active margins Where: Drowned forests and marsh deposits covered by layers of tsunami- deposited sand along the coasts of northern California, Oregon, and Washington testify to long periods of slow coastal uplift separated by episodes of rapid subsidence during large earthquake Long-term subsidence?
Predict where a flood-tide delta will form and explain how and why its size differs from an ebb-tide delta. (page 269)
Where is forms: where sand carried by long-shore currents reaches a tidal inlet and the incoming tide pushed it landward through the inlet, the rising tide carries sand into the lagoon and settles, sand transported out of the lagoon by an ebbing tide sometimes forms an ebb-tide on the seaward side of a barrier island How its size differs from an ebb-tide delta: larger than ebb-tide. Why its size differs from an ebb-tide delta: ebb-tides are reworked by waves in the open marine environment and because the outgoing tide usually has a lower sediment-transport capacity than the incoming tide- outgoing currents are slower than the incoming current
Make a sketch showing the three most important geomorphic features of an uplifting coast.
pg.412
Explain why topography can be used to map the underlying bedrock structure and lithology in some areas but not in others?
stuff that buries underlying bedrock has a different shape than what's underneath in high relief , rapidly uplifting areas ( there is no relationship)
Explain why only half the sediment shed off the Andes makes it to the Ocean?
Because convergent boundary, part gets subducted some gets stored at the base of the mountain
Define "legacy sediment."
Decades' to century worth of sediment deposition from when a landscape was cleared previously.
Compare emergent and submergent coastlines and explain the processes that lead to these two different types of coasts (page 254)
Emergent coastlines: stretches of the coast that have been exposed by relative sea-level fall Submergent coastlines: those that have been inundated by the sea due to a relative rise in sea level Processes: can be local or global, change in volume and size of ice sheets, continental erosion, (local) uplift or subsidence driven by plate tectonics or by isostatic responses to loading and unloading over long time scales
Explain the feedback mechanism that encourages gorge formation and deepening.
Gorge formation: variety of bedrock incision processes via. plucking, pithole formation and abrasion , stream power creates loop this gives rise to positive feedback that enhances incision Deepening:
Explain how and why floodplain morphology changes downstream.
How: floodplains get wider due to characteristics( ex. Grain size) of fluvial sediment that systematically change downstream , slope can be expected to change downstream Why: flow changes adjust
How do hillslopes respond to increasing uplift rates? (page 413)
In low to moderate gradient landscape, slope steepness generally increases with increasing uplift rates, until a characteristic threshold or subthreshold slopes develops
List three different base levels and describe what processes might lead them to change over time.
Increase decrease or stay the same over time based on 3 changes : climate, tectonics and isostasy 1.Natural lake 2. Dam 3.Ocean
What are the geomorphic expressions of joints and in what climate zones are such expressions easier to detect?(page 411)
Joints can greatly influence differential weathering and erosion because they provide conduits along which water and plant roots can penetrate and break up and erode rock masses Climate zones: arid environments with bedrock hillslopes
Explain, from a process perspective, the reason that river-dominated, wave-dominated, and tide-dominated deltas have different shapes.
River-dominated deltas have different shapes:low wave energy, low tidal range, high sediment supply, Wave- dominated deltas have different shapes: high wave energy, unidirectional longshore transport , steep offshore slopes Tide-dominated deltas have different shapes: low wave energy, high tidal range, little longshore transport
Given two examples of how ocean circulation affects terrestrial climate and explain how each works (page 436)
North Atlantic - you have the formation of cold, salty, dense water are part of the oceans thermohaline circulation, the sinking of this water frive s currents and delivery of tropical warmth if it got colder- glacial margins will advance Heinrich event- flooding of the north atlantic by fresh less dense glacial meltwater can alter ocean heat flow
Explain how oxygen isotopes can be used to infer paleoclimatic changes using two different geologic archives
Oxygen isotope ratio can be used as a proxy to indicate past climates 1.Can be found in the shells of marine organisms 2.Found in signature trapped within an ice core Lower ratio of 18O/16O correlates with lower ocean temperatures The ratio of stable oxygen isotopes in the shells can be interpreted as a paleothermometer and a measure of global ice volume Use it to determine past ocean temperatures and past climates
Define and contrast steady-state and transient landscapes?
Steady-state landscapes- overall characteristics don't change significantly over time. Tectonic Transient landscapes are those in the process of responding to a change in base level, uplift rate, or climate.In transient response vary with location because it takes time to propagate Transient - the period of response to change This lag results in the Delta s = zero and selta s= not zero The distinction between steady-state and transient landscapes depends on timescale. Equilibrium or steady-state land forms dominantly reflect the processes involved in shaping them. Transient landforms bear a strong imprint of the landscape history.
What caused lakes to form in arid southwestern North America during the last glaciation?
The maximum extent of the glacier caused the climate to change which created more rainfall which added to the pluvial lakes
What is the most common relict landscape?
The most common relict landscapes are formerly glaciated regions out of equilibrium with the post-glacial climate. The topography we see are from processes in the past. Like the swiss alps and once glaciated sierra nevada are formed from processes no longer relevant
Provide examples of steady-state and transient landscapes.
Transient Landscape- New Zealand were steep slopes and earthflows resulting from incision triggered by uplift and base-level fall. Steady-State- Organ coast range, tawan , Newzeland Straight Mountain slopes at Lindis Pass in the Southern Alps, South Island, New Zealand, an area where rock uplift and erosion rates are thought to be closely matched.
Predict the geomorphic effect of installing a jetty or a groin in the coastal zone(p. 263)
*concrete structures that project from the shoreline into the sea with the purpose of intercepting sediment moving along the coast Jetty: leads to a zone of sediment accumulation on their upcurrent side and a zone of erosion on their sediment starved, downcurrent side Groins: sediment accumulates on the upcurrent sides of grpins while longshore transport continues to move sediment away from their downcurrent side
What are the geomorphic effects, both near the coast and inland, of changing sea level over time?
1. barrier islands are created when sea levels were lower and are now moving shoreward as sea levels continue to rise 2.During periods of lower sea level large portions of continental shelves are exposed
Draw a diagram showing how sediment yield might change over time as forests are cleared and land is developed.
Fg. 7.11 Pg 241
What can be learned from the longitudinal profiles of a river?(page 413)
Figure 12B1 Can identify where faults or lithology(the study of the general physical characteristics of rocks) might be influencing channel slope Example: in response to localized steepening of the profile braided channels tend to increase and convert to a single-thread channel
Provide examples to explain why erosion rates vary over time in some landscapes and not in others.
Glaciers in Himalayas Gradient changes - Appila were once steep and now they are very gentle In some landscapes are in Erosion rates tend to scale with rates of tectonic forcing. Rapidly uplifting areas tend to erode quickly, and tectonically quiescent areas tend to erode more slowly. Likewise, steeper slopes and higher-relief terrain tend to be correlated with higher erosion rates. Short term and long term are comprable As are those from astralia
