Questions and Answers of Geomorphology The Mechanics And Chemistry Of Landscapes

Estimate the duration of the Lake Bonneville flood, given the volume available between Bonneville and Provo shorelines, and the estimated peak discharge. Report your answer in years.(a) How much
You are the mayor of a town immediately downstream from a glacier with a side-glacier lake that could catastrophically drain through a subglacial tunnel. The geometry of the lake basin is such that
Consider a changing world in which the coverage of the Arctic Ocean by sea ice is shrinking, as revealed in Figure 16.26. Discuss several feedbacks by which this should accelerate coastal erosion,
Discuss how the changes in the distribution of waves revealed in Figure 16.30 might alter the coastlines they impact.Figure 16.30 Number 103 10 101 10 10 10 10 10 10 10 10 10 Buoy #44004 (CAPE MAY)
On a shelf sloping at 10 m/km, calculate the greatest rate of shoreline transgression associated with post-LGM sea level rise.
How would the heights of tides differ if the Moon were closer to the Earth? At the current recession rate of 3.8 cm/yr, how might the tides differ between now and 2 Ga? (The assumption of a steady
6. Predict the storm surge associated with a Category 4 hurricane, due to:i) The low pressure of the eye of the storm?ii) Sustained winds of 100 mph (=160 km/hr)How far up the Mississippi river would
Contrast the power arriving in waves generated from two storms at sea, one in which the significant wave height is H = 3 m, traveling at a group speed of 20 m/s, the other with wave height of H = 4
Predict the spatial down-coast pattern of littoral drift on a 50 km reach of coast, assuming that the littoral cell is in steady state. Assume that the backwearing rate of the bounding 10-m tall
Hyperpycnal flows. Calculate the concentration of quartz sediment necessary to make the bulk density of river water equal to that of seawater (1003 kg/m3). Concentrations exceeding this will generate
Calculate the total volume of water (in km3) that must have been added to the global oceans to cause the sea level rise associated with meltwater pulse Ia.
The steric effect. Calculate the expected rise in sea level if the global ocean were to warm by 1°C. Use the mean depth of the ocean to be 3800 m, and the coefficient of thermal expansion to be
Develop a strategy for documenting the conditions under which the rocks of Racetrack Playa move. Ultimately, we must capture these in motion, and I am interested in what proposals you might have for
How many sand grains are there in a one-grain diameter wide cross section of a simple 10 cm wavelength ripple. Assume that the ripple is 5 mm in height, and 10 cm long, and can be approximated as a
Calculate the residence time of a sand grain in a barchan dune. The footprint of the dune is 75 m long in the wind direction, and repeat photos have shown that the dune is moving at 15 m/year. For
Calculate the wind speed required to move one of the Racetrack Playa rocks. Assume that the rock is rectangular, with sides of 30 cm, and height of 20 cm, and that it is a limestone. Assume that the
Analyze the washboard road figure (15.16) for speed of translation of the ripples.
Wind erosion. Calculate the ratio of the wind erosion that might be expected in the same site in winds that differ by a factor of two. Assume the lower wind condition is twice that needed to entrain
Calculate the expected celerity of an eolian ripple, in cm/hr, if the ripple is 1 cm tall (a typical ripple) and the average sand discharge over the hour of measurement is 5x10-6 m3/m/s.
Calculate the expected celerity of an eolian sand dune, in m/yr, if the dune is 5 m tall (a typical barchan) and the annual average sand discharge is 2.5x10-6 m3/m/s.
Given the theory of suspended sediment transport we have discussed, develop a means by which one could measure the total suspended sediment discharge at a given position on a river given only one
What flow depth is required in a turbulent river to support quartz grains of diameter 0.25 mm in suspension if the slope of the river is 1 m/km. Assume that the critical Rouse number for suspension
How much higher would saltation curtain be on Mars than on Earth? Assume that the distribution of particle launch speeds and angles would be the same as on Earth; for simplicity, let us take the
What is the response time, tr, for quartz in air for the following grain sizes: 10, 100, 300 microns. And for the same grains in water?
Long term transport. We wish to know the total transport of sand in an eolian system over the course of an entire year. You know that the threshold shear velocity for entrainment is u* = 0.3 m/s for
Ignoring air drag, calculate the speeds (in m/s) and angles at which a baseball must leave the bat in order to clear an outfield wall 15 ft high and 400 feet. The ball is launched from 2 feet above
How much time is a grain in the air if it is launched at a speed of 0.5 m/s at an angle of 45° with respect to the horizontal? Repeat the calculation for a grain launched at a speed of 1 m/s at 60°.
Calculate the depth of water flow in a wide channel (the stage) that would be necessary to entrain 2 mm quartz grains from the bed, given that the slope of the river is 2 m/km. Take the Shield’s
Discuss how a bedrock river should respond to glacial-interglacial fluctuations in base level of order 120 m. What legacy of the glacial sea level low stand might be seen in the present profile or
Consider a bedrock river with a longitudinal profile that displays a strong convexity well upstream of its mouth. How would you discriminate between the possibilities that this convexity is due to 1)
Consider a simple semicircular channel in bedrock. If we assume that erosion rate of the bedrock floor is governed by the local shear stress exerted by the flow on the bed, and we further assume that
The river erosion rate estimates we obtain from strath terraces are averages over the time since the terrace was abandoned by the river. If the erosion of the river downward into rock occurs only
Can we use the stream power formulation for bedrock erosion in a vertical waterfall? Why or why not? Think about what the slope of the waterfall is, and calculate the expected lowering rate of the
Again referring to Figure 13.3, discuss how different the interpretation of Kings Canyon evolution can be given that we have dated several caves rather than simply Bat Cave, or Boyden Cave.Figure
If the stream power formulation captures the essence of the bedrock river incision problem, will the effect of ponding of water behind a landslide dam, and then suddenly releasing it in a
In Figure 13.16 we depict how the Wind River in Wyoming steepens as it passes through Wind River Canyon. Say the gradient of the stream changes by 5-fold. Assuming that the river has achieved a
In Figure 13.3 we illustrate the incision history of Kings River as deduced by dating of caves embedded in the valley walls. For the sample from Bats Cave which is shown as having been abandoned at
Calculate the mean rate of lowering of the channel floor in shale badlands in which the lowering is accomplished entirely through passage of small knickpoints. You measure the step heights to be 20
In using the stream power formulation in bedrock incision problems, we are assuming that some fraction of the potential energy released by dropping the parcel of water in elevation is used to work on
Consider a strath terrace along a river etching into bedrock. We have determined its age to be 130 ka using 10Be concentrations in the sediment capping the terrace. It is presently 55 m above the
At the historical rate of retreat of Niagara Falls, how long will it take for the falls to reach Lake Erie?
Graph the expected history of retreat of a river knickpoint in which the distribution of basin area is A=5(L-x)1/2, where the length of the full channel is L, and x is the distance upstream from the
Discuss how rivers might differ if the fluid being transported were of a different density or viscosity or both. And lest you think this silly, we are learning about a landscape on Titan that appears
Estimate the mean residence time of a sand grain on a floodplain. Assume that the sand grain was deposited in a scrollbar deposit as the river meandered within the floodplain. The floodplain is
For a given discharge of a river, calculate and plot the dependence of the river stage on the roughness of the bed of the river. This is relevant to management plans for how to modify the river to
You now obtain a water sample of the same river from a specific depth, 10 cm above the bed, and have its grain-size distribution analyzed.There are three primary grain diameters involved (all quartz;
Suspended sediment in rivers. Consider a steep-walled river channel with a width of 50 m, a bankfull depth of 3 m (to the levee tops), and a slope of 0.5 m/km (i.e., note that this is the tangent of
Mississippi River velocity structure and sediment transport. We are given a set of measurements of the flow velocity within a profile of the Mississippi River, at the time flowing with an approximate
A commonly used bedload transport formula in fluvial settings is the Meyer-Peter-Muller formula. One version of this is simply:Q=A(tb-tc)3/2, where A = 0.04 (and the units of A work out such that Q
You are asked to assess the maximum diameter grain capable of being entrained in a particular flow. The flow is 2 m deep, the slope of the channel is 0.002, and the particles are granitic and
Estimate the time it takes for a water molecule to travel from the tip of the Amazon to the ocean.
What happens in the aftermath of a fire on steep hillsides? Describe how this might affect the runoff generation mechanism, and the types of sediment yields from the source? See John McPhee’s
What runoff mechanisms might have dominated the Earth’s surface before grasses evolved? And how might their evolution have altered the runoff and sediment yields from landscapes?
Discuss how paving a hillslope would alter the hydrology of the bounding stream.
Describe qualitatively how the runoff from a landscape will differ under these circumstances: steady rainfall, increasing rainfall through time during the storm, different starting moisture content.
Create your own fractal drainage network, using a generator function of your own design. Can you generate something that looks like the Appalachicola network shown in Figure 11.23? Why or why
If the critical shear stress for entrainment of grains from the slope is 0.7 Pa, how far from the divide must one go to find entrainment in the case shown in Figure 11.17? This is Horton’s Xc.
In the above question, calculate the thickness of the steady state overland flow at the base of the slope if the slope is uniform at 8° and the Darcy-Weisbach friction coefficient f = 0.3.
Calculate of steady state water discharge at the base of a hillslope. The hillslope is 150 m long, the rainfall rate is 7 mm/hr and the rain has been falling for long enough that the hydrology of the
Plot the Dupuit solution for the groundwater field between two channels 200 m apart. Assume that the rainfall rate is 5 mm/hr, and that the hydraulic conductivity of the uniform substrate is 20
How fast did the front of the flash flood depicted in Figure 11.4 travel, if the distance between gage a and gage d is 580 m?Figure 11.4 (a) of volume Percent 60 50 40 30 20 10 0 clay porosity, field
What water tension (negative pressure) must a plant be able to produce in order to utilize water in a sandy loam soil with a moisture content of 15%?
Consider a soil dominated by fine sand. Find its porosity, field capacity, and permanent wilting point. Given these values, how much water will be available for plant growth per square meter of land
Consider a thin flow of water on a smooth slope. The slope is 10°, and the thickness of the flow is measured to be 4 mm. Calculate the mean speed of the flow and assess whether the flow will be
How might the odd spiky landscape illustrated in the photograph at the start of the chapter, from the Tsingy Park in Madagascar form? It certainly violates our expectation of convex hilltops! What
Explain as simply as you can why a compacted granular material is less likely to fail catastrophically on a slope than is a loosely packed material.
Consider the plot of landslide areas in Figure 10.37. Assess the slope of the straight-line fit to the data, and report the resulting probability density function for landslide area.Figure 10.37
Runout of a large landslide. Consider a landslide mass that fails from an elevation of 2500 m. The valley floor onto which the rockmass tumbles lies at 1700 m. The mass comes to a screeching halt on
Slope stability. Consider a long linear hillslope with a slope angle of 25°. It has soil that is 1 m thick, and a shear test on the soil reveals its internal angle of friction is 31°, a cohesion
Steady regolith discharge. On a 150 long hillslope, regolith is being generated at a uniform rate of 40 microns/yr. Calculate and plot the distribution of downslope regolith discharge with distance
On a hillslope with a weathering rate of 20 microns/yr and an effective hillslope diffusivity of 0.02 m2/yr, what is the expected curvature of the hillslope? Plot the full profile if the summit of
How much strain does a soil sustain from the growth of tree roots? Assume that the tree roots are 10 cm in diameter, are simple vertical taproots, and are spaced at 1.5 m spacing. (Obviously this is
Plot the expected steady state pattern (as a function of distance from the crest) of discharge of regolith on a convex hillslope in a climate in which the production rate of regolith is 20 mm/yr.
On a hillslope with regolith 1.2 m thick, and regolith production rate of 8 μm/yr, what is the mean residence time of regolith in the regolith column?Now you note that this slope is 100 m long and
If it takes 2 hours to bake a turkey with a radius of 20 cm, how long would it take to bake one that has a radius of 25 cm? Present your formula and your reasoning, not just the answer.
Ignoring the role of latent heat, calculate the thickness of the active layer at the same site as in problem 1. Assume that the amplitude (half the full range) of the temperature swing at the surface
Estimate the flow law parameter A from the ice speed profile of the Worthington Glacier in Figure 8.12b. Assume the local slope of the glacier at the borehole location to be 60 m/km, and that the ice
Estimate the flow law parameter A from the ice speed profile of the Worthington Glacier in Figure 8.12b. Assume the local slope of the glacier at the borehole location to be 60 m/km, and that the ice
Convert a thermal diffusivity k = 1 mm2/s into m2/yr.
You have now gone through the agony of processing the sample and have had it analyzed at the Purdue PRIME lab. They report back to you (months later) a concentration from which you calculate that the
On the Huon Peninsula of Papua New Guinea, a set of coral marine terraces grace the coastline. These are datable using U/Th methods, and have yielded good dates back to several hundred thousand
How much new water must be added to the ocean each year to sustain the measured 2 mm/yr rate of rise attributable to new water? Give your answer in both cubic km and gigatonnes.
What is the mean density of the Earth?
Given the map of the expected response to the Lake Ojibway flood reproduced in Figure 17.15, where would be a good site to measure the true sea level rise associated with the flood?Figure 17.15 180W
Calculate the peak discharge to be expected from the proposed catastrophic refilling of the Black Sea through the Bosporus Strait. Assume that the minimum width of the strait is 700 m, and the
Imagine that you are a manager in a town downstream from a moraineponded lake. Discuss the strategy you would use to assess the height above the river that you would deem “safe” in the advent of
Estimate the background “inheritance” of 10Be in the Highway 1 terrace profile (Figure 18.11), and use this to estimate the mean erosion rate in the catchments that once supplying beach sand to
Advection and uplift. Given the slip rate, V, of the San Andreas Fault, and a stationary rock uplift pattern tied to a bend in the fault represented by what is the total uplift one would expect by
Using the plot in Figure 18.4, estimate how many coseismic uplift events the Highway 1 terrace must have experienced in order to reach its present elevation in the middle of the Aptos Arch. You will
What is your favorite flood tale? Summarize its main features, how we know about it, and review the evidence we use to deduce its peak discharge.
If the waves arriving at the coast have a 10 second period, coastal retreat rate is 20 cm/yr, and the horizontal exponential length scale for decay of flex-swaying of the cliffs by the load of the
If the 10Be concentration in littoral sand is 1x105 atoms/gram quartz, that in river sand is 1x104 atoms/gram quartz and the mean 10Be in terrace deposits atop the backwearing cliffs is 2x105
If the CRN-derived age of the terrace is 80 ka, and the terrace sand is 1.5 m thick, and has a bulk density of 2000 kg/m3, what is the mean concentration of 10Be in the terrace sands.
Discuss why the Santa Cruz Mountains, which rise more than 1 km above sea level, are not terraced from bottom to top? In other words, why do the terraces end in the landscape at some elevation
Given the slightly negative slope of the phase boundary between liquid water and ice in Figure 1.2, how much would the pressure-melting point of ice be depressed at the base of an ice sheet 1 km
Based upon the δ18O curve, how much colder, in °C, is the Earth surface now than at the Eocene Climatic Optimum shown in Figure 1.3? And in °F?Figure 1.3 K/T Age (Ma) 5
The relative concentrations of 18O vs 16O in shells and in ice are used as climate proxies. The main process that drives the largest of the signals in the ocean is what we call fractionation during
Calculate the global average terrestrial erosion rate over the last 5 Ma based upon the 31x1018 kg of sediment delivered to the oceans in the most recent 5 Ma bin in Figure 1.5.Figure 1.5 Mass of
Compare the total energy available to the Earth surface from below and from above. At this distance form the Sun, the solar energy flux is roughly 1370 W/m2. The global mean heat flux from Earth’s
Catalog the changes in the geomorphic system that you might imagine could be induced by a warming climate. We would hope you would have a longer list after reading the entire book!

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