Mathematical Methods in Geology GEOL MAMAL 595 Text

Mathematical Methods in Geology GEOL MA/MAL 595 Text: Mathematics, A Simple Tool for Geologists by David Waltham

What is Quantitative About a Volcanic Eruption ?

Course Goals * To improve simple math concepts and tools by using them with geological examples * Improve your ability to apply math to geological problems * Think of mathematics as a language - method of communication - must take each lesson one at a time - skipping lessons can lead to frustration

Traditional Geology is often “Qualitative” - What happened ? - What is the order or sequence of events ?

Let's Look at This Problem “Quanitatively” What time did the man die ? What is his temperature now ? What was the location of the man when he was killed ?

Example of a Sedimentary Basin What can we say about this sedimentary basin? How is sediment traveling in this lake bed ? What is the order of deposition ? Can we say anything else ?

Sedimentary Basin: A More Quantitative Approach Which sediment layer is oldest, youngest ? Does this suggest a relationship between depth and age ? Assuming the sedimentation rate is constant, how could we write this relationship ?

Sedimentary Basin: A More Quantitative Approach Which sediment layer is oldest, youngest ? Does this suggest a relationship between depth and age ? Assuming the sedimentation rate is constant, how could we write this relationship ?

Proportionality Constant If Depth increases, how does Age change ? Depth is proportional to Age if both increase. Let Depth be described in meters and Age in years. If one meter of sediment is deposited in one year, what is the constant of proportionality ? If two meters of sediment is deposited in one year, what is the constant of proportionality ?

Proportionality Constant We can replace the words with letters: Depth = D Age = A What are the units of k ? The constant, k, tells us how rapidly sediments accumulate. What does a large value of k tell us about accumulation ? What does a small value of k tell us ?

Magnetic Reversals Recorded in Lake Sediments Mono Lake, California: If 4 centimeters (cm) were deposited in one yr, what was the rate of sedimentation ? Pyramid Lake, Nevada: The sediment layer of magnetization is much thinner in Lake Pyramid than observed in Lake Mono. What may have caused this ? If 2 cm were deposited in one yr, what was the rate of sedimentation in Pyramid Lake ? (Actual estimated rates are much slower 25 cm/kyr and 12 cm/kyr)

Quantifying Geological Processes You have just produced mathematical expressions relating geological variables. Did we gain anything from this effort ? D= k. A Was the accuracy of our estimates improved ? Only SOMETIMES ! Sometimes a mathematical expression won't tell you anything you don't already know. But the ease of manipulating or re-arranging an equation can often give us new insight into geological processes. Mathematical equations are also very consistent. (Same data –> same answer)

Quantifying Geological Processes Mathematical expressions can be tested. D= k. A Expressions developed from known data can be used to make predictions of data we don't have yet – that are difficult to measure. In the previous example, you could predict the age of a particular deposit in Mono Lake. You could then test this prediction by obtaining a geochemical dating method. Example – earthquake hazard – Chino Earthquake - movie.

Can Mathematics be Wrong ? D= k. A What could we have overlooked in this example ? Are there other physical properties of this problem which could change our results or calculations ? Mathematical equations are rarely 100% correct (almost never)! We hope that if the expressions represent the major physical properties of the system, that the results will be close.

How to Solve Problems What is a problem ? - By definition, “an obstacle which makes it difficult to achieve a desired goal, objective, or purpose” (Wikipedia) literally: “obstacle” Etymology: from proballein to throw forward from pro- forward and ballein to throw (Merriam-Webster) A “Little Problem” - just a little difficult A “Great Problem” - very difficult - Some degree of difficulty belongs to every notion of a problem - Where there is no difficulty, there is no problem.

How to Solve Problems Four Step approach: Read / Understand the problem - “Know-how” (practical experience) is most valuable tool - Write down/discuss what (anything) you know about the problem - Draw a picture or sketch - Write down what you don't know - Write down what you want to find Devise a Plan Carry out the Plan - Write explanation of everything you do - Use written explanations of equations - Should have more text than math Look back at your work

A Few Example Problems: 1. A bird trying to find his partner, starting walking from point P, and walked one meter due north. Then he changed direction and walked one meter due east. Then he turned again to the right and walked one meter due south, and arrived exactly at the point P he started from. What color was the bird ? Why didn't he fly the route ? To solve a problem use the steps we discussed: 2. Paul piece of land, you exactly has 1. wants Make aa list of anything knowlevel, aboutwhich this problem north-south, east-west, each 2. Makeand a listthe of two whatothers you doexactly not know, what youand need to find boundary line measures exactlyof 100 ft. Can Paul buy 3. DRAW a simple picture the problem! such athen. . . piece of land in the U. S. ? 4. Devise a plan to solve the problem 5. Carry out your plan 6. Look back at your work.

A Few Example Problems: 2. Paul wants a piece of land, exactly level, which has four boundary lines. Two boundary lines run exactly north-south, and the two others exactly east-west, and each boundary line measures exactly 100 ft. Can Paul buy such a piece of land in the U. S. ?