Volcano Morphology:
Morphology is the study of form and structure. Over 90% of all volcanoes can be classified into one of six morphological types. These types are…
Shield Volcanoes: Shield volcanoes are formed when fluid basalt lava comes out of the earth. As basalt-type lava is especially fluid, these types of volcanoes are not very steep. Examples include Kilauea and Mauna Loa in Hawaii.
Stratovolcanoes (also called Composite Volcanoes): Stratovolcanoes are formed from andesite and dacite lava. These lavas are cooler and less fluid than basalt lava. Because the lava is viscous, these volcanoes often build up pressure and produce explosive eruptions. Often these volcanoes are made up of layers of lava and pyroclastic material (volcanic fragments, crystals, ash, pumice and glass shards). For this reason they are often called composite volcanoes. Examples include Mount St. Helens and Mount Rainier.
The other four types do not look like typical volcanoes…
Rhyolite caldera complexes: These volcanoes consist of huge magma chambers and when they erupt, the eruption often falls into itself leaving no mountain-like trace. These are the most explosive of volcanoes. Examples include Yellowstone.
Monogenetic fields: With these volcanoes, the lava moves very slowly so no pipe work of lava tubes is formed and the lava simply spreads over the region from numerous vents. Examples include the San Francisco volcanic field.
Flood Basalts: With these volcanoes, lava flows outward and covers a large area (some are thousands of kilometers in size). These flows can also be thick – lava forces into an originally thin flow. The Columbia River Basalt Province covers most of SE Washington State and extends to the Pacific and into Oregon.
Mid-Ocean Ridges: The earth surface is composed of tectonic plates – large slabs of solid rock that move. When these tectonic plates spread apart, basalt lava wells to the earth’s surface – the region where this upsurge of lava is occurring is called a mid-ocean ridge. Examples include the Juan de Fuca Ridge which extends along the western coast of the United States.
Source of educational material: http://volcano.oregonstate.edu/types-volcanoes
LOGGING THE CACHE
To get credit for this earth cache, go to the posted coordinates. Using the description above and the vista and information at the coordinates, complete the following questions and send the answers to the cache owner. Please include your cacher name and also this geocache’s name in your message. After that, you are welcome to log the cache. If you'd like, you are welcome to include a picture from your visit with your log but this is not a logging requirement.
-
From your vista, locate Crater Lake. Mount Mazama, the precursor to Crater Lake, was what type of volcano?
Given Mount Mazama’s morphological type, explain why it makes sense that Mount Mazama became Crater Lake.
-
Look across the from the posted coordinates and identify the mountain to the far right. This is Mount Bailey, nicknamed "Old Baldy."
Using the geocache description and the mountain's appearance, what do you think is the morphological type of this volcano?
Given its type, why does the mountain's nickname make sense?
-
Look across the lake and identify Timber Crater and Hemlock Butte. Based upon the appearance of these peaks, what do you think is the morphological type of each mountain? Why?
-
Look across the lake and identify Mount Thielson. How is the appearance of Thielson is different than the other volcanoes in your view.
Mount Thielson is a stratovolcano or composite volcano. How do you think this volcano's morphological type contributed to its current unique appearance?