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Chapter 6: Up from the Inferno: Magma and Igneous Rocks

Geotours

Download Geotours.

Getting Started :

If you haven’t done it already, download Google Earth™ and install it on your computer.
If you haven’t done it already, download the Geotours.kmz file and save a copy to your desktop. (The Geotours.kmz file contains the Geotours for all chapters, so you only need to download this once!)
By downloading Geotours.kmz you acknowledge that it was created solely to accompany Steve Marshak's Earth: Portrait of a Planet and Essentials of Geology and is limited to use with only Steve Marshak's Earth: Portrait of a Planet and Essentials of Geology and may not be reproduced, stored in a retrieval system, or transmitted in any form by any means for any other purpose without the written permission of the publisher.
Double-click the Geotours.kmz file and Google Earth™ will open automatically.
In the left-hand sidebar you will see a Places menu, and in the Temporary Places folder you will see an EARTH_3e.kmz file. Double-click the file and you will see a list of Geotours for each chapter.
Then open the Geotour folder you want to explore! If you’d like to read more about the features of Geotours see Using Geotours, or go to our Helpful Resources section.

STOPS ON GEOTOUR 6: Exposures of Igneous Rocks

Yosemite National Park, California

See also Worksheet Problem 1, Problem Bonus: Polygon Outlines: Sierra Nevada Batholith and Henry Mts. Laccolith Complex
"What a Geologist Sees" Geofeatures: Bridalveil Falls hanging valley, El Capitan, Half Dome: Joint: Exfoliation Joints, and Roche Mountonnée

Shiprock, New Mexico

See also Worksheet Problem 2
"What a Geologist Sees" Geofeatures: Volcanic Neck and three Radial Dikes

Izalco Volcano, El Salvador

See also Worksheet Problems 3-4

Dikes, Western Australia
Cinder Cones, Arizona

See also Worksheet Problems 5-6

GEOTOUR 6 WORKSHEET

What do igneous rocks look like in the field? They are exposed in many places around the world. In this Geotour, we take you to see a few of the better examples.

Yosemite National Park, California
1. Yosemite National Park provides spectacular glaciated exposures of granite comprising the Sierra Nevada batholith. Many separate plutons form the batholith.

(a) Fly to Image G6.1. To give a sense of the minimum thickness of the mass of granite, determine the elevation difference (m) between the floor of Yosemite Valley and the top of Half Dome.

(b) Click on the red polygon for the Sierra Nevada batholith in the folder labeled Problem 1. You will see the western United States (from an elevation of ~900 km). Using the transparency slider at the bottom of the Places panel, you can make the polygon transparent. To get a sense of the size of this batholith, determine its length (in km).

(c) Click on the polygon labeled Henry Mountains Laccolith Complex. This complex consists of blister-like intrusions (note that this complex is much smaller than the previous batholith). Double-click on the placemark for Problem 1c to zoom down to 7 km to look at the laccolith on the east side of the central part of the complex (if you turn on the “Geographic Features” layer, you can see that this laccolith lies just west of Raggy Canyon). Color contrasts define a circular pattern of rock layers outlining the laccolith. Explain why this pattern exists:

Shiprock, New Mexico
2. The dikes near Shiprock intruded into sedimentary beds. Heat from the dikes baked and altered immediately adjacent sedimentary rock. Match the placemarks labeled Problem 2a, b, and c to the positions of corresponding rock type.

• unaltered sedimentary rock
• dike
• baked sedimentary rock

Izalco Volcano, El Salvador
3. Fly to Image G6.5. You can recognize different types of recent volcanic rocks by their texture on the landscape. Deposits of lapilli (fragmental debris) that fall from the air form a smooth apron centered at the volcano’s crater. Lava flows tend to have fingers and channels parallel to the flow direction. Click on the placemarks labeled Problem 3a and b, and identify which rock type occurs at which site.

• lapilli
• lava flow

4. Which location (placemark for Problem 4a or b) is more likely to be affected by lahar flows associated with an eruption of Izalco Volcano?

Cinder Cones, Arizona
5. Fly to Image G6.8 to see SP Crater, a cinder cone comprised predominantly of pyroclastic material. Notably, after this cinder cone had formed, a basaltic lava flow erupted. Click on the placemark for Problem 5 to see this flow more clearly.

(a) Did the lava erupt from the summit or the side of the volcano, and in which overall direction did it flow? (Note that there are some small side flows off the main flow.)

(b) How long is the flow (in km)?

(c) SP Crater has the youngest eruption in the area. What feature of the landscape leads to this conclusion? (Hint: Zoom up to an elevation of about 30 to 40 km and compare the color of different flows.)

6. Double-click on the placemark for Problem 6. From this vantage, you can see that the cone of SP Crater is not perfectly symmetric. Which side of the cone is wider? Explain why this asymmetry exists. (Hint: Think about the material that comprises SP Crater.)

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StudySpace: Chemistry 2e.