Geological Exploration of Metro Cleveland (GEM-C)
The Geological Exploration of Metro Cleveland tour is a series of Earthcaches which help to illustrate some geology that is hidden within the urban downtown area of Cleveland. These urban earthcaches help to highlight a wide variety of geological topics that are hidden in plain sight - in fact thousands of people walk by these stones every day without so much as a second thought about their origins!
This tour does not need to be done in any particular order and each earthcache is a standalone lesson. As you wander through the streets of Cleveland take a moment to pause and reflect on the lessons you can learn in just a normal city block!
In mine and road-cutting
Canal and drainage ditch
With his feet and with his fingers
He teased out the secrets
Long hidden by Mother Nature
-Excerpt from "Where Giants Lay Buried" by Lewis Entwistle
As with all earthcaches there is no container to find here, rather you must read through the description below and answer a few questions in order to log this cache as found. Please ensure that you send your answers to the CO via email or message in a timely fashion.
The Key Tower
Bordering the north side of Public Square, where you now stand, is the 10-story Key Tower Building, Cleveland's oldest skyscraper. The original building opened in 1890. The base and columns of this building are made of pink Precambrian-age Graniteville granite, however the exterior walls are composed of red sandstone which is where our lesson today will focus.
The bright red stone before you are a naturally occurring stone known as Jacobsville Sandstone dating from approximately 800 MYA. It was originally quarried by the Portage Entry Red Stone Company in Houghton County, Michigan. It is composed primarily of grains of quartz and feldspar. Its deep red color is due to the presence of hematite. One characteristic aspect of this rock are small white circles which are the result of coloration leeching which occurred as a result of organic inclusions which settled into the sandstone layers as the rock was formed. As the rock is a sandstone, it is prone to a very specific type of erosion, which we'll discuss in more detail below.
Spalling
Spalling is a term for a specific type of erosion wherein water seeps between layers of stone depositing salt crystals which, over time, slowly grow and wedge the layers apart. In addition to spreading caused by salt intrusion, during Ohio's winters when freezing weather happens, water expands by up to 9% as it crystalizes into ice, further expanding and degrading the stone.
While water is the primary cause for spalling to occur, building technique can increase the likelihood of it happening as well. As a general rule of thumb, spalling typically occurs first on ledges where the stone is less protected and more exposed. Additionally, if a builder stacks sandstone blocks with their beds vertical and parallel to the building's surface (like an upright book stacked with its cover face out on a book shelf) then these erosive agents can weaken the stone so that the beds peel off one layer at a time. If however the beds are laid horizontally (like a book flat on a shelf) water has a harder time penetrating the layers.
Below: An example of spalling occuring after a fire in the wilderness. While spalling in an urban environment is typically caused when water acts as an erosive agent, in the wilderness fire and extreme heat can cause the same effect.
Logging Requirements
- Examine the stones before you. Do you see any inclusions? Estimate the average size.
- Do you see any examples of spalling erosion? (hint: look around the doors and windows)
- Why do you think this part of the stone is eroding this way?
- How thick are the layers that are separating?
- Post a photo of yourself or a personal geocaching item at GZ.
References:
- https://dam.assets.ohio.gov/image/upload/ohiodnr.gov/documents/geology/GB5_Hannibal_1992.pdf
- Seattle Walks: Discovering History and Nature in the City by David B Williams.
- Vine, James D. (1969), Geology and Coal Resources of the Cumberland, Hobart, and Maple Valley Quadrangles, King County, Washington, vol. Professional Paper 624, U. S. Geological Survey