Ketchikan, Alaska's first city is a place of many wonders. On Revillagigedo Island, known as The Rock, Ketchikan has a long history as a fishing, lumber and tourist town.
The island is composed of Igneous, Sedimentary and Volcanic rock but the town is built on metamorphic rock formed by heat and pressure and shaped by glaciers and erosion.
Igneous rocks are those that solidify from magma, a molten mixture of rock-forming minerals and usually volatiles such as gases and steam. Since their constituent minerals are crystallized from molten material, igneous rocks are formed at high temperatures. They originate from processes deep within the Earth—typically at depths of about 50 to 200 kilometres (30 to 120 miles)—in the mid- to lower-crust or in the upper mantle. Igneous rocks are subdivided into two categories: intrusive (emplaced in the crust), and extrusive (extruded onto the surface of the land or ocean bottom), in which case the cooling molten material is called lava.
Sedimentary rocks are those that are deposited and lithified (compacted and cemented together) at the Earth’s surface, with the assistance of running water, wind, ice, or living organisms. Most are deposited from the land surface to the bottoms of lakes, rivers, and oceans. Sedimentary rocks are generally stratified—i.e., they have layering. Layers may be distinguished by differences in colour, particle size, type of cement, or internal arrangement.
Metamorphic rocks are those formed by changes in preexisting rocks under the influence of high temperature, pressure, and chemically active solutions. The changes can be chemical (compositional) and physical (textural) in character. Metamorphic rocks are often formed by processes deep within the Earth that produce new minerals, textures, and crystal structures. The recrystallization that takes place does so essentially in the solid state, rather than by complete remelting, and can be aided by ductile deformation and the presence of interstitial fluids such as water. Metamorphism often produces apparent layering, or banding, because of the segregation of minerals into separate bands. Metamorphic processes can also occur at the Earth’s surface due to meteorite impact events and pyrometamorphism taking place near burning coal seams ignited by lightning strikes.
Unique to Ketchikan is the one-way tunnel completed in 1954 to make driving along the waterfront easier to reach Newtown from Downtown. A return road was later built skirting the tunnel and there are homes with street access atop Knob Hill. This makes it the the only tunnel one can drive over, around and through.
There are web cams on the city web site the second of which shows the tunnel.
CLICK HERE TO SEE WEB CAMS
In order to claim this Earthcache as Found, you must do some research reading and visit the tunnel
Send me a message describing the rock near the mouth of the tunnel or along the "around" sidewalk with your impression of the type of rock you see. Additionally POST a photo of your GPS, a trackable or yourself with the tunnel. you may use a web cam shot captured from the city website,
References;
Klein, C. and Carmichael, . Robert S. (2022, October 19). rock. Encyclopedia Britannica. https://www.britannica.com/science/rock-geology
Sculptures in Granite prepared by USFS available at the Southwest Alaska Discover Center in Ketchikan or https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fseprd629659.pdf
http://www.sitnews.net/JuneAllen/Tunnel/040903_Ketchikan_Tunnel.html