Astronomy 23/223 Homework:

Geologic Mapping on Venus

In class we looked at examples of several of the geological formations that are found on the surface of Venus...

Impact craters (of course) are caused by impacts; on Venus there are only 963 of them, 2-280 km in size, of which 6 are multi-ring craters, each 100-300 km diameter. To look at other craters, check out these images of Stuart, Piaf, and a tiny crater with no name (only a number) called V44-C6.

Tesserae (Tt) are a type of terrain composed of complex deformation patterns, with intensely crinkled landscapes, that form very rough surfaces with boulders 0.1 m or larger.

Dark parabolas are features shaped roughly like parabolas around volcanoes. They are caused by wind-blown, fine-grained erupted material that falls around the source, smoothing the surface so it appears dark on radar images. Because the prevailing winds on Venus always blow from east to west, they usually form to the west of craters.

Pit chains are collapse structures that form along grabens, or down-dropped trenches (along areas of extension), when loose surface material falls into pits along the depression.

Densely fractured plains (Pdf) contain parallel, densely-spaced faults from extension and shearing; they cover 3% of surface, and are the first unit after the tessera.

Fractured and ridged plains (Pfr) are broad, 10-15 km ridges that are interpreted to be compressional folds

Wrinkle ridge plains (Pwr) are one of the most common units on Venus; they rise ~1 km above surrounding plains and may be stacks of thin sheets of flows. They occur in lowland plains, and contain 1-2 km wide folds.

Lobate Plains (Pl) are fans of superposed lava flows emanating from specific source. They are usually associated with rifts or coronae, with some large volcanoes.

Shield plains (Psh) are clusters of coalescing, gently sloping volcanic shields that also occur on flanks of larger shield volcanoes. They have small collapse pits at centers, and are typically 3-20 km in diameter.


In this homework, you will use these images to help you understand one of the first geological quadrangles to be mapped on Venus, designated V20. This work was done by George McGill at the University of Massachusetts, who has very kindly made this material available to us. Note that the lower left corner of this map is 0N, 0E. First, take a look at this colored image of the topography of the area; in these images, the color changes from purple (low) to blue to green to yellow to orange to red (pink; high).

Note that some areas on all the maps are empty (showing as black or dark green in the topographic image), due to incomplete coverage of satellite data. You’re looking at an area of volcanoes of various sizes. Contrast this image with the radar image shown below (in black and white); remember, radar images show surface roughness/smoothness, NOT topography.

When looking at radar images, it is easy to make the assumption that "dark" areas represent visually dark material (like the lunar maria plains), while "light" represents visually light material (the highlands of the moon). THIS IS NOT TRUE FOR RADAR! Dark images on the radar maps correspond to smooth areas (like a lava flow) while white images refer to rough areas (like fault ridges).

The full radar image of this quadrangle is 134 Mb at 72 dots per inch; these maps represent huge amounts of data! To make looking at the map a little easier, we’ve broken it down into a smaller, low resolution version of the whole thing, as well as high resolution files (16 of them), starting with tile V20_1 in the upper left hand corner, and ending with tile V20_16 in the lower left. To make yourself a big map, you can print out all 20 tiles and then tape them together. However, it shouldn’t be necessary to print the whole thing out to answer the homework questions.

Here are the images:

A. Entire quadrangle (low resolution)


J. Tile V20_9


B. Tile V20_1


K. Tile V20_10


C. Tile V20_2


L. Tile V20_11


D. Tile V20_3


M. Tile V20_12


E. Tile V20_4


N. Tile V20_13


F. Tile V20_5


O. Tile V20_14


G. Tile V20_6


P. Tile V20_15


H. Tile V20_7


Q. Tile V20_16


I. Tile V20_8 R. Labeled radar map with names of features



For this assignment, you will use these maps and some close-up images from them to answer the following questions:

1. Locate a dark parabola on the radar map, sketch it or print it out, and name the tile(s) on which it appears. What feature causes a dark parabola? On which tile does this causing feature appear?
2. Locate a pancake dome, sketch it or print it out, and name the tile(s) on which it appears. Why do pancake domes appear on Venus and not any other planet?
3. Rank the relative ages of the following features on this map (A, B, C, D, and E), which was extracted from a higher resolution version of this quadrangle, and indicate your reasoning in assigning these relative ages.
4. Using the labeled radar map and the topologic map, give the names of the highest and lowest features on this map.
5. What’s the difference between the east and west ends of this lava flow? Remember that this is a radar image and not an optical one.
6. Examine this map (again a close-up of the V20 quad) and rank the relative ages of features A, B, and C.

Home | Syllabus | Course Schedule | Images and Data | Homework | Homework Answers
In-Class Exercises | In-Class Answers | Exam Review | Exam Answers | Student List | Contact Darby

| Summer Internships | More on Astronomy| Bus Schedule

This page was created by Darby Dyar and is maintained by Darby Dyar and Rebekah Robson-May.
Last updated on 28 November, 2005 .