Homework #0 Humphrey Geology 4880 Fall 20172016

This is due next ThursdayTuesday (Sept 76).

Notes on all homework:

This course deviates from most courses in that it recognizes that the world around us is complex, and that therefore questions and answers must only be approximations. Learning to answer approximate questions in a reasonable way is fundamental in learning how to ask questions about how our world works. It is both more advanced and more difficult than “plug and chug” homework, since you will have to think more.

Try to couch your answers at the appropriate level of accuracy that is implied by the question. You are free to use data from any source or to make reasonable assumptions, but state what you assume, or show the data you use and give the source of the data. Be aware that data and ideas from the Web are of highly variable quality, so if you use web sources you must include the URLs. To do the homework you will have to take 4 steps:

· figure out how to do the problem,

· decide on the data you need (if any),

· collect the necessary information,

· and finally produce an answer, or more likely, a discussion of a possible answer. Note for these questions I expect an answer based on your thinking. If by chance you actually find an answer to a question on the Web, I will expect you to explain the answer.

Your work must be neat, legible, and organized. I am not willing to wade through a mess and I will just give it back to you to re-do. You can work with others, but be aware that you will have to do similar questions on exams and quizzes, by yourself.

Often the homework will include one or more questions that are quite hard. Warning, usually the last one(s) are virtually impossible; however I expect an attempt, since I want to see how you approach a difficult question. (Homework #0 does not have an impossible last question, but all the questions should make you think). Note that these questions are mostly just to get you thinking in the wide ranging style that is needed to solve a lot of geomorphic type questions. Actual answers only need to be (or for that matter can only be) approximate. Since it is early in the course, these questions do not require deep geomorphic knowledge, but do introduce several concepts in geomorphology and environmental Geology.

If you stumped by a question, I am totally willing to discuss the problem.

Now the actual homework

1

· Part 1 How much rock is in Medicine Bow Peak? To make it more precise: what is the mass in kilograms of Medicine Bow peak, above the elevation of Gap Lake (the lake between Medicine Bow Peak and Browns Peak)? You will need a topo map. TopoQuest on the web is a good place to look. For other views Google Earth is a fantastic tool. [You will have to decide how accurately you want to make this estimate. A general rule of thumb: there is no point in making any measurement that is significantly more accurate than any other variable in the problem. Part 2 asks you to think about this a bit more]

· Part 2 Now include an educated comment on the likely size of the error in your estimate. Again, to be precise, answer these questions:

i. What are the 3 largest potential sources of error in your estimate, in order of importance. (Note this is a straightforward question, but introduces the difficulty of answering real world problems. Include your working so I can follow your method)

ii. Based on your answer to the previous, what digit of your answer will each of the 3 errors affect. For example, a factor of 2 error would affect the first digit, while a 10% (or 0.1) type of error would affect the second digitput a % value on the potential size of the largest error, with a comment on why you think that % is reasonable.

iii. Look at your answer to part 1. How many significant digits should be in your answer.

22 Afternoon thunderstorms are common at this time of year in Laramie. How many raindrops hit Laramie during a typical Laramie thunderstorm? List the assumptions you had to make. (This is an exercise in reasonable assumptions)

3 Close to ½ the surface of the earth has been transformed by human activity. One of the spatially largest activities is deforestation. Removing a forest tends to raise the albedo of the land and thus more sunlight is reflected from the earth, which in turn should cool the global climate. So could we reverse our current global warming trend by cutting down trees? Give at least one pro and one con argument.

Write a comment on this idea: is it true (Note, please don’t talk about the ethics of this, I am asking for a factual or logical answer)? Part of the reason for asking this question is that you will probably find several well written but opposite viewpoints in the literature and especially on the web. I want to illustrate that many simple questions do not have a single ‘correct’ answer. Note that there really is an answer; if we did cut down all the trees, the temperature will either go up or down. (But can we really know the answer now, without cutting down trees?)

34 An interesting little factoid is that tire dust is a notable source of air pollution (mainly because it is chemically reactive, especially with ozone in the air). It is mainly a problem in urban environments. But a lot of vehicles drive on I-80. How many kilograms of tire dust is produced in the Wyoming segment of I-80 in a year, just by the 18 wheel trucks?

4 Over the long weekend we got a lot of forest fire smoke in the air. When I returned from the Rocky Mountain Field Trip in my plane on Monday, I only managed to see the airport at Laramie from 2 miles away! I wondered how much smoke there had to be in the air so that I could only see 2 miles. Although there is a lot of chemical ‘soup’ in the smoke, the biggest part is small (1 micron sized) bits of organic carbon. My thinking was that if I could only see only 2 miles, then that meant that a photon traveling 2 miles in air had a very good chance of hitting a smoke particle before it reached my eye. So my question to you (using the above assumptions): How many smoke particles were in 1 cubic meter of Laramie air on Monday?

5 (hard) Sand sized particles are common in the weathered surface material of our planet. Sand is common everywhere that physical (as opposed to chemical) weathering occurs, such as in rivers, beaches and deserts. Indeed, virtually all surficial deposits, that are not marine, have a strong peak in the sand size of the distribution. Laramie overlies a large indurated pile of sand, the Casper sandstone. This has economic ramifications since gravel costs about twice as much as sand. About $7Billion of sand and gravel are used in construction, compared to about $25Billion of all other minerals mined in the US.

Question: Why is sand so common, and why is sand all about the same size? Or, why isn’t there a continuum or smooth distribution of sizes from big to tiny, instead of this preponderance of sand? (as it turns out there is another peak in abundance in the silt/clay sizes). Hint, note I said that sand is common where physical erosion processes dominate.