Little Sweden Tuff vs. Debris Flow
Latitude: 38.137861; Longitude: -120.090613
The Little Sweden overlook is located off of Highway 108, 3 miles west of Cold Springs and 7 miles west of Pinecrest, California (see Figure 1). The EarthCache site is directly off of Highway 108 on a large, safe turnout (with an incredible view!) and the terrain rating is = 1. The geological features geologists have been curious about here are in the cliff outcrop across the highway, which are also evident in the boulders at the GPS location. You will observe the rocks at the EarthCache turnout and compare/contrast them to see how nature behaved in the geological past – you may be surprised!
Figure 1: Location of the Little Sweden Tuff vs. Debris Flow EarthCache on Highway 108, east of Long Barn and west of Pinecrest, CA.
This EarthCache is similar in some ways to the Trail of the Gargoyles (TOG) EarthCache (EC), nearby, in terms of how the rocks at each site formed. One of the rock types is quite different than those found at TOG and this EC focuses, in part, on the distinction between the two. The Little Walker Volcanic Center/Caldera, which existed east of the current location of Sonora Pass when it was active approximately 10 million years ago (+/- a few million years), produced younger volcanic rocks that cover older granitic rocks in the high Sierra. The two large boulders at the GPS location ultimately came from the Little Walker Volcanic Center/Caldera, one was erupted into the air, then deposited onto the land surface (see Figure 2). The other was deposited as volcanic debris that flowed down a stream channel, then solidified and lithified (turned to stone). The older granitic rock that underlies the younger volcanic rock, is approximately 100 million years old, while the volcanic rock is approximately 10 million years old. Layers of the volcanic rock are exposed in outcrop across Highway 108 from the Little Sweden overlook (see Figure 3).
Figure 2: Two different rock types at Latitude: 38.137861; Longitude: -120.090613 (note dog "Sunshine" and foot/shoe for scale).
Figure 3: Roadcut showing layers of extrusive volcanic material deposited by the Little Walker Volcanic Center/Caldera along Highway 108 at Little Sweden. A layer of volcanic airfall tuff is visible at the road level and a layer of volcanic debris flow material overlies the tuff.
When volcanologists study the deposits from volcanoes, they carefully observe the characteristics of the rocks, including the textures/grain sizes and the mineral composition/color. For this EarthCache you will observe the textures of the 2 rocks at the GPS location, specifically the sphericity – how rounded or angular the particles (called clasts) are. To do this, you will need the Sphericity vs. Roundness scale geologists use (see Figure 4).
Figure 4: Rounding, Grain Size, and Sorting Classification.
The two rock types are shown in the close up below (see Figure 5) for comparison. The one on the left is a volcanic tuff and the one on the right is a volcanic debris flow. The tuff on the left is composed of volcanic particles of pumice (light colored clasts) suspended in volcanic ash, that settled from air fallout. Pumice is basically frozen lava froth (like root beer foam) that solidified in the air – it has lots of vesicles (or gas pockets) that make it low density and light weight. Volcanic debris flows are sometimes called lahars and are the result of the interaction of water and volcanic rock. Snow or glacial ice at the top of a volcano can be melted by an eruption, forming a slurry of rock material that flows rapidly down the flanks of a volcano into nearby stream channels. Volcanic debris flows can also form from intense rainfall events that mobilize the loose volcanic eruptive products into nearby stream channels. Which rock has the rounder particles? Why?
Figure 5: Image shows a close up of Figure 2 and the 2 rocks to be assessed for sphericity/roundness. The rock on the left if volcanic airfall tuff. The rock on the right is a volcanic debris flow that settled in a stream valley.
EARTH SCIENCE BIG IDEAS
The Earth Science education community put together 9 “Big Ideas” for the Earth Science Literacy Initiative (ESLI), shown below. Their purpose was to highlight the main concepts and ideas a person should understand to be literate in the earth sciences:
An Earth-science-literate person:
• understands the fundamental concepts of Earth’s many systems
• knows how to find and assess scientifically credible information about Earth
• communicates about Earth science in a meaningful way
• is able to make informed and responsible decisions regarding Earth and its resources
Which of these Big Ideas below do you think are most relevant to this EarthCache?
Earth Science Literacy Project:
1. Big Idea 1: Earth scientists use repeatable observations and testable ideas to understand and explain our planet.
2. Big Idea 2: Earth is 4.6 billion years old.
3. Big Idea 3: Earth is a complex system of interacting rock, water, air, and life.
4. Big Idea 4: Earth is continuously changing.
5. Big Idea 5: Earth is the water planet.
6. Big Idea 6: Life evolves on a dynamic Earth and continuously modifies Earth.
7. Big Idea 7: Humans depend on Earth for resources.
8. Big Idea 8: Natural Hazards pose risks to humans.
9. Big Idea 9: Humans significantly alter the Earth.
GEOPRINCIPLES
There are several fundamental principles, developed over time, that guide geological reasoning and critical thinking, listed below. Read each short description, then use your best judgement to determine which principle, or principles, best relate to this EarthCache.
7 Principles in Geology:
1. Superposition – the oldest strata are at the bottom of the sequence
2. Original Horizontality - layers of sediment are originally deposited horizontally
3. Lateral Continuity - layers of sediment initially extend laterally in all directions
4. Faunal Succession - fossils succeed each other vertically in a specific, reliable order that can be identified over wide horizontal distances
5. Law of Intrusive Relationships - the geologic feature which cuts another is the younger of the two features
6. Uniformitarianism - the assumption that the same natural laws and processes that operate in the universe now have always operated in the universe in the past and apply everywhere in the universe
7. Catastrophism - the theory that the Earth has been affected in the past by sudden, short-lived, violent events, possibly worldwide in scope
LOGISTICS AND SAFETY
This EarthCache is located approximately 0.25 miles on a paved trail at an visitor overlook and is closed for half of the year or more, depending on the amount of snow in the area. The area is rugged and without cell phone service. EarthCachers should take great care in terms of safety while enjoying this cache.
Visitors to this site should plan ahead and prepare by:
• Knowing the regulations and special concerns for the area you are planning to visit (obeying laws that prohibit collection or destruction of artifacts);
• Carrying a map and a GPS unit and/or compass;
• Staying on existing roads and trails;
• Staying away from any/all mine shafts and adits;
• Planning for extreme weather, hazards, and emergencies;
• Being aware that cell phones DO NOT usually work in the rural areas away from the major highways;
• Leaving your travel plans with a responsible party, including the date and time of your return;
• Being aware of any natural hazards associated with the region (e.g. poison oak, rattlesnakes, mosquitoes, cliffs/steep slopes, etc., etc);
• Carrying a full-size spare tire, extra food, water, and warm clothing;
• Following the “Tread Lightly" and "Leave No Trace” philosophy.
TO LOG THIS EARTHCACHE INCLUDE
1. The name of this EarthCache on the first line of your email.
2. The number of people in your group.
3. Using the roundness scale provided, you will measure and estimate the sphericity (roundness vs. angularity) of the particles (called clasts) in the 2 rock samples at the EarthCache GPS location.
4. After determining the sphericity clasts observed, notice which rock formed as an airfall tuff and which formed from a volcanic debris flow. How does the sphericity relate to whether the rock was deposited by air or water?
5. Which Big Ideas (1-9) are connected (list)?
6. Which GeoPrinciples (1-7) are relevant (list)?
7. Include a photo or 2 if you're so inclined (optional).
Note: In order to manage email volume, you may assume your responses are accurate if you do not get an email after logging this EarthCache. If a response is grossly inaccurate, you will not receive credit for the cache.
Note: For a brief summary of the geologic history of the Central Sierra, see this EarthCache:
Dragoon Gulch EarthCache
REFERENCES
1. Alden, Andrew, “Igneous Rock Classification Diagrams”, (2008), licensed to About.com, https://www.thoughtco.com/igneous-rock-classification-diagrams-4122900, updated February 24, 2019.
2. Busby, Cathy, (2006), “Mapping of Cenozoic Volcanic Rocks in the Central High Sierra: Clues to Understanding Landscape Evolution and Range-Front Faulting (pp. 1-54), , in "Geology of the Central Sierra"; Editor for the National Association of Geoscience Teachers Far
Western Section Fall 2006 Conference Guidebook; 2006; 161 pp.; Columbia College, September 29-October 1, 2006, Tolhurst, J., editor.
3. Domokos G, Jerolmack DJ, Sipos AÁ, Török Á, 2014, “How River Rocks Round: Resolving the Shape-Size Paradox”, PLoS ONE 9(2): e88657, https://doi.org/10.1371/journal.pone.0088657.
4. East Carolina University, 2010, “Grain Size Distribution”, Introduction to Depositional Systems and Grains, Geology 4010/4011, date last revised: 08/20/2010, GEOLOGY 4010/4111, http://core.ecu.edu/geology/rigsbyc/rigsby/Sedimentology/2010/sedsyl.htm.
5. Ransome, Fredrick Leslie, (1898), “Some Lava Flows of the Western Slope of the Sierra Nevada, California”, Washington, DC, Government Printing Office, US Geological Survey bulletin., United States Geological Survey, 89.