Volcanism:
In contrast to the relatively low lying lava tubes, fields and the occasional lava meteor, Big Southern Butte stands up from the landscape. "Rhyolitic hills occur in several places in the eastern Snake River Plain. One of the most prominent is Big Southern Butte. It rises 760 meters above the plain, is 6.5 kilometers across, and comprises 2 coalesced cumulo domes of 0.3 million-year-old rhyolite and an elevated section of older basalt flows" (*1). Big Southern Butte is rich in obsidian, Image 12 below illustrates the formation of a volcanic Dome as found in the Snake River Plain and best typified by the Big Southern Butte. Image 50 also illustrates the Dome formation and the overlying Snake Plain arc. Image 24 outlines a cross section of several Domes found in the Plain area including Big Southern Butte and Cedar Butte.
Geology:
Rhyolite Example: SRP
Image 53
Example of two states of volcanic lava flow when cooled and crystalized at different rates. Cooled quickly, vitrophyre, is the glassy obsidian form (bottom layer) of rhyolite while the slowly cooled rhyolite apprears more red to brown similar to granite. The photo (Image 53, area near Twin Falls in the SRP) shows a stacked dome where lava from the same "magma batch" formed at the same time yet resulted in vastly different properties (*15).
Park Imagery:
Big Southern Butte National Monument established in 1976 comprises over 5,500 acres of federal land within the Snake River Plain. This area is representative of the youngest volcanic rocks found anywhere in the US (*14).
Processed Imagery:
Image 32 below is a portion of a false color composite obtained from the Digital Geology of Idaho. Big Southern Butte is labeled to the center east of the image.
Historic Photos: Big Southern Butte
Image 51
Big Southern Butte provided Native Americans obsidian for use in weapons and hunting. Obsidian is a volcanic rock also found throughout Wyoming, Montana and California. Near what is now Big Southern Butte, an ancient lake (Lake Terreton 1.8 mya-10,000 years ago) provided resources in the form of a shallow inland lake and adjacent wetland environment. Image 51 is a collection of imagery represented in the area of Big Southern Butte. Items 2 and 4 represent the ancient lake environment and tools made from locally found obsidian (*13).