Introduction
Rose diagrams are used for graphic representation of compass directions and orientations of a variety of field data. A rose diagram is a full 360o circle with subdivisions associated with the “bearing.” North, east, south, and west are represented by 0o (or 360o), 90o, 180o, and 270o, respectively. Therefore, northwest is 315o, southeast is 135o, and so on. You can use rose diagrams to represent wind direction, speed, wave approach, paleocurrent flow (e.g., in an ancient river or a tidal channel), movement of glaciers, and attitude of geologic structures.
In this exercise, you will learn how to construct rose diagrams using collected data, and interpret them in a real-world setting. Your up-to-date knowledge of sediment textures and their significance is also tested in this lab.
Exercise
Procedure: The data on the last two pages are field measurements of wind direction, wind speed (power), and orientation of glacial striations (scratches on glacially-scoured bedrock). Combine all the data into 10o intervals (e.g. a tally chart where counts 11o through 20o are within a 10-20o interval, while 21o is in a 20-30o interval, etc). On a blank rose diagram (on page 3), assign a number of field measurements to a length of the radial axis (straight line going through the center of the circle). For example, if each data value is represented by 1 cm, four identical values will be shown as 4 cm pie slices for the 10o interval these data fall into. You should end up with three rose diagrams showing directions of: 1) wind duration data; 2) wind speed, and 3) glacial striations (you will see in a minute how to solve geologic problems).
e-ROSES: You can copy the azimuth data into an Excel and use any rose diagram software to make your plots. See example below:
Questions
Using the first set of data you plotted the directions from which winds blow most of the time at Philadelphia Airport during the year. These are called prevailing winds. The second diagram indicates the compass directions of the most powerful (>20 mph) dominant winds or storm winds in the same area. Use these plots to answer the following questions:
- What is the direction of prevailing winds in this area (N, NW, SE, etc)? __
- Where do most stormy winds come from? __
USE YOUR ANSWERS ABOVE TO ANSWER THESE QUESTIONS:
Using the map on page 4 of Cape Cod (Massachusetts) answer the following:
- Some of the world’s thickest dunes are located at point D. Knowing that sand needs to be dry to be blown in a wind, which location was most likely contributing sand to the dunefield (use one letter: A, B, C, or E):
Why? ________________________
- If the glacial sediments are being eroded from the bluffs at point G and transported alongshore to form the Race Run, and eventually the Long Point, the sediment will be
coarsest at (A, B, C, or E) _ and the finest at _ - The submerged bedrock outcrop is located at X. Knowing that the glacial striations on top of it have two opposite directions (as any line will), and using your knowledge of the real world, what was the direction of ice movement in North America based on your third rose-diagram)?
Ice came from the (use SE, W, E, etc.): __ - Using examples of unidirectional (A) and bi-directional (B) diagrams on the top left of your rose diagram answer page, which plot (answer A or B) reflects the signatures of the following transport agents:
a. River Current
b. Tidal Flow
c. Wave Action
d. Mudslide
FIELD DATA
Wind Duration Wind Speed Glacial Striations1 298 043 124
2 092 048 035
3 316 314 034
4 176 205 178
5 226 312 165
6 098 000 012
7 314 273 003
8 317 046 178
9 228 039 009
10 013 057 125
11 002 357 003
12 256 215 165
13 345 238 168
14 276 049 007
15 135 126 180
16 187 238 172
17 165 173 180
18 038 042 180
19 074 098 170
20 154 056 025
21 234 218 015
22 319 063 030
23 243 097 043
24 319 100 171
25 317 245 167
26 098 048 179
27 318 032 154
28 276 257 006
29 196 328 006
30 125 038 016
31 094 327 156
32 054 344 026
33 023 070 175
34 317 176 164
35 226 078 180
36 319 043 002
37 054 062 176
38 316 042 177
39 227 041 174
40 228 314 165
41 317 253 003
42 071 165 180
43 005 187 179
44 122 276 179
45 156 042 169
46 318 075 171
47 134 039 175
48 176 045 174
49 317 047 176
50 358 321 111
Sample Solution
