theImage.com     Notes on Basic Geology
Notes created & information organization based on the book:
"The Dynamic Earth - an introduction to physical geology"
Brian Skinner & Stephen C. Porter   (further book information here)
also look at www.wiley.com for additional resource information
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Volcanoes & Magma - Page 3

Shield volcanoes occur when very fluid, but non explosive lava rises up and pours out in a number of events. they are formed over time by the fluid lava building up in layer after layer on the flanks of he volcano. Since the lavas are quite fluid they may flow for long distances, and the sides of shield volcanoes tend to have low slope angles, but may be miles across.

Built on many repeating layers of previous fluidized lava flows.

Mauna Loa Volcano, Hawaii- Shield Volcano

Image: U.S. Department of Interior,
U.S. Geological Survey
Tephra Cones
When gases are released from a magma in a controlled but rapid fashion, the material produced is cooled during its flight, but is not thrown far. This cooled material forms a granular mass around the vent and produce a cone, the slope are typically about 30 degrees. This is the slope that the rock can hold via friction, any higher and it tumbles down until it once again achieves about 30 degrees.

(Pu`u ka Pele) was erupted low on the southeast flank of Mauna Kea Volcano.

Image: U.S. Department of Interior,
U.S. Geological Survey
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