Just in time for International EarthCache Day which is celebrated on October 8th, 2023. Each year, it falls on the first Sunday of Earth Science Week as a new way to learn about the earth. For those not in the know, EarthCaches are special geological locations anyone can visit to learn about our planet.
This Earthcache is located near South Twin Lake, Oregon. It is accessible from multiple directions, just choose your route carefully as the distance may be short, but the hike up or down the hill is the reason for the higher terrain rating. The coordinates will take you to a general viewpoint and area to explore. The answers to the questions will be found within a 25 yard diameter of GZ. If you haven't already found it, here will be your chance to nab the Ambush (GCJ6B1) geocache as well.
Objectives:
1. To see in your mind's eye how this geologic formation came to be created in Oregon
2. To identify the major types of geologic factors such as glaciers, eruptions, floods, erosion and weathering that occured at this location
A brief synapisis of one piece of Oregon's geologic history
Once upon a time, when dinasaurs roamed Montana, there was no Oregon. In those days, the waves of the Pacific ocean broke on the shores of Idaho. The mountains of Oregon lay far offshore, as coral fringed islands in a shallow sea. Even after the sea subsided and land emerged, the great glaciers covered the mountain tops and carved valleys carrying with them rock rubble known as morraines and rock flour that was ground down by ice, rain and winds and deposited as thick blankets of silt called loess. These mountain glacier deposits can be found throughout the Cascade mountains. As the glaciers melted they formed giant lakes, often miles long that occupied much of Oregon. [2]
During the Palegogene era, about10-15 million years ago the Three Sisters Cascade volcanoes were erupting, alternating between lava flows and explosive eruptions of ash, pumice and broken lava. While the volcanoes were erupting, much of Oregon was still underwater with ancient lakes. These inland waters deposited sand and gravel, mud and clay into the valleys and basins. Over millions of years, these deposits have been cemented and compacted in to soft rock and in some areas have been uplifted from their original position and then eroded away. In many places the rocks are layered with lava flows and volcanic deposits from violent nearby eruptions. Evidence of an ancient lake or seabed filled with sandstone, siltstone, mudstone, claystone and conglomerate is present at this location. [1]
Weathering vs. Erosion
Weathering is the deterioration of rocks, soils and minerals through through contact with water, atmospheric gases and biological organisms. Weathering occurs in situ (on-site with little or no movement) and so is distinct from erosion which involves the transport of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity.
Weathering processes are divided into physical and chemical weathering. Physical weathering involves the breakdown of rocks and soils through the effects of heat, water, ice or other agents. Living organisms may contribute to physical weathering, as well. Wedging by plant roots, which sometimes enter cracks in rocks and pry them apart. The burrowing of worms or other animals may also help disintegrate rock, as can "plucking" by lichens.Chemical weathering involves the chemical reaction of water, atmospheric gases, and biologically produced chemicals with rocks and soils. Water is the principal agent behind both physical and chemical weathering, though atmospheric oxygen and carbon dioxide and the activities of biological organisms are also important. [4]
Erosion is the action of water flow or wind that removes soil, rock or dissolved material from one location on the Earth's crust and then transports it to another location where it is deposited. Erosion is distinct from weathering which involves no movement.
The process of mountain block uplift is important in exposing new rock strata to the atmosphere and moisture, enabling Phsyical, chemical weathering and erosion to occur.The materials left over after the rock breaks down combine with organic material to create soil. Many of Earth's landforms and landscapes are the result of weathering processes combined with erosion and re-deposition. [3]
IN ORDER TO LOG THIS EARTHCACHE AS A "FIND", YOU MUST EMAIL OR MESSAGE THE CACHE OWNER THE ANSWERS TO ANY ONE OF THE FOUR QUESTIONS BELOW. You choose your level of desired difficulty e.g. Freshman, Sophomore, Graduate, or PhD level So Pick one and answer those questions in order to satisfy the requirements and claim this Earthcache
When you message me include the following:
The name of this earthcache: Terraphobia
Group answers are fine; just let me know who was with you and the date you found it.
Freshman level
1a. From where you are standing estimate the height of the closest formation. What does that tell you about the ancient lake or seabed.
1b. Why do you think this formation is separate from the others?
Sophomore level
2a. Look at the formation, how many layers are present.
2b. Were these formations caused primarily by weathering or errosion?
Graduate level
3a Describe the make up and layers of the closest formation, including the color and size of the particals. Do you see evidence of a volcanic explosion within the layers?
3b. What do you think caused the various layers in the formation.
PhD Level
4a. Based on the cache description and your own observations, describe how this unique geologic structure camed to be formed at this location. Why do you think there are no other similar formations nearby?
Extra credit
Post a picture of you, or your GPS or a travelbug and describe if you approached the formation from the South, East, West or North and how would you describe your chosen route in.
Sources:
1.Oregon: A geologic History by the Oregon Department of Geology and Mineral Indicustries.
2. In search of ancient Oregon: A geological and Natural History by Ellen Morris Bishop
3. Erosion. Wikipedia. https://en.wikipedia.org/wiki/Erosion
4. Weathering. Wikipedia. https://en.wikipedia.org/wiki/Weathering