NOTE: Simply visiting the site is not enough to claim a find (per earthcaching guidelines) - you must message/email answers to the cache owner in a timely fashion. After one week if I haven't received answers I will send you a reminder, if no response after that, the log will unfortunately be deleted.
The Mono-Inyo Craters form the southern part of a volcanic chain that stretches 25 miles north-to-south from Mono Lake to Mammoth Mountain along the western edge of the Long Valley Caldera, one of the Earth’s largest calderas.
Between 550 and 650 years ago, a dike of magma formed below Deer Mountain which caused significant ground cracking and fault formation. As the magma continued to rise, it superheated subsurface groundwater resulting in a tremendous buildup of pressure and subsequent violent eruption. Steam-driven volcanic eruptions of this kind are known as phreatic eruptions and are the kind believed to be responsible for the eruption of Krakatoa in 1883.
The two southernmost Inyo Craters (referred to as North and South Crater) are ~700’ in diameter and have a depth of ~200’. Each contains a small lake (also called a maar) at the bottom, as opposed to the third explosion crater (appropriately named Summit Crater) near the summit of Deer Mountain which is dry. Other volcanic features in the Mono-Inyo chain (such as Obsidian Dome) were similarly initiated by phreatic eruptions, but in outward appearance stand in stark contrast to the Inyo Craters. An earthcache at Obsidian Dome five miles north of here stands for reference.
Directions to the Inyo Craters: From Mammoth Scenic Loop, turn onto Inyo Craters Road at N 37 40.897 W 118 59.679 and follow your GPS to the visitor parking area (N 37 41.310 W 119 00.347). NOTE: Inyo Craters Road is unpaved and is not plowed in the winter. From the trailhead in the parking lot, a 0.3 mile hike takes you to the plaque at the rim of South Crater (posted coordinates). North Crater is ~500' north of the posted coordinates. If you're feeling adventurous, continue a further 0.4 mile up to the rim of Summit Crater (N 37 41.794 W 119 00.692) for some truly spectacular views of this volcanic landscape.
To log this earthcache, please email me (use my geocaching profile) the answers to ALL the following questions (locations of answers are in brackets) and please do NOT post answers in your found log:
1. The Inyo Craters and Obsidian Dome were both formed by phreatic eruptions, likely from the same magma dike. Explain why the former is crater-like in appearance while the latter is dome-like. [trailhead kiosk]
2. How far was some of the rock ejected in these eruptions? [trailhead kiosk]
3. Which crater is the youngest of the three (South, North, or Summit Crater)? [posted coordinates]
4. Who is mentioned in the last sentence on the plaque? [posted coordinates]
The Obsidian Dome earthcache may also be a useful reference for question #1. Photos at the site are encouraged.
Enjoy your visit, and many thanks to Jon at the Inyo National Forest, with whose permission this earthcache was placed.
References:
1. U. S. Geological Survey, in particular the information on volcanoes
2. Inyo National Forest