BOLTS of SNOT--Hermanus EarthCache

This earthcache will require that you learn how to make a field geologist's sketch, to learn about local geology, identify different types of rocks, and then to create a sketch identifying some a local geological features. You will then take a photograph of or scan that sketch and submit it to me via e-mail in order to successfully complete the educational tasks of this earthcache. This earthcache has a high difficulty rating due to the logging requirements.

This is one of two BOLTS of SNOT earthcaches I have placed in South Africa--the other is BOLTS of SNOT--Cape Town. While the BOLTS of SNOT are common to each, the type of geology—and therefore the Terminology and Geology sections—differs in each case. If you complete both of the BOLTS of SNOT earthcaches you will have learned about two very different geological features and will have used your field geologist's skills to record your knowledge. The difficult for this is set to 4 because of the work involved in completing the BOLTS of SNOT portion of the task.

The coordinates for the geocache will require you to park nearby and make your way first down a staircase to the beach, then along the rocks. Please be aware of the tides and plan your trip accordingly. The waves here can be treacherous, and the rocks can be slippery. When you reach ground zero you should face the cliff, with your back to the ocean. You will be staring at a unique geological feature—the intersection of two very obviously different types of rocks.

There are three sections to this earthcache, each of which you will needs to review in order to submit your answers. While you can easily do this on-site, you will likely be better-served by reading through the sections before you arrive at GZ. This will help you complete the earthcache a bit more quickly. Once on-site you will need to have the list of terms in Section II handy. Finally, before setting out you should skip down to the "Requirements for Logging This Cache" section to get a better understanding of the final tasks.

The sections:

I. Explanation of BOLTS of SNOT
II. Terminology
III. Geology of Hermanus and Southern Africa

Equipment You will need the following equipment in order to complete this Earthcache:

• GPS unit;
• Pencil or pen;
• Paper;
• Camera-equipped cellphone, or a scanner.

Section I—BOLTS of SNOT

Earth science is a field of study that often requires scientists to record observations in the field that they can then take back to the laboratory. For hundreds of years field scientists used field sketches and diagrams to record their observations for later study. Nowadays, of course, people can use cameras to record images with some precision. However, a field sketch is still a handy tool, especially for students and Earthcachers.

In the earth sciences, these field sketches are detail renditions of an area of study. Usually a simple line drawing of a geological feature made with pencil or pen on paper, the sketch provides as much detail as possible. So the sketcher does not need to be an artist, simply thorough.

From Learning Space:

Drawing a sketch is one of the best ways to start [studying a feature], as it forces you to notice many aspects of the exposure. It also helps you to build up a picture of which aspects are significant and which are incidental or even irrelevant to a geological study. The aim of a field sketch is that it provides a record of your observations [. . .]

• Spend a minute or so looking carefully at the rock face to begin to recognise some general details.
• Now it is time to start committing some of your observations to paper! Draw in the skyline and the base of the exposure. This marks out the area that you have to concentrate on.
• Sketch in the main features using simple lines wherever possible. If necessary, rub out and redraw particular areas until you're happy with them. Part of the skill of making successful geological observations of complex exposures is to follow any key feature (the top or bottom of a sedimentary bed, for instance), as far as you can with your eye until it disappears from view. Similarly, the skill of making an effective geological sketch is to draw a discrete, continuous line (where the feature is continuous), rather than to sketch a vague series of unconnected lines. Ignore shadows from sunlight and features such as loose boulders, fallen branches, etc. You can indicate any patches of vegetation using your own simple symbols for grass, trees, etc.
• Label the features you have drawn.

There is also a pretty good PDF here that details how to draw a field sketch.

A sketch is not enough. The details of the feature need to be categorized and labeled for later study. The technique for labeling goes by different names, the two most common of which are BOLTS and SNOT, and they are an important part of life in the field for earth scientists. The two acronyms stand for:

• Border: This is the frame that surrounds a diagram or map
• Orientation: A marker that shows the cardinal direction of North
• Legend: A key, usually in the corner of the diagram, showing what the symbols in the diagram mean
• Title: The title of the diagram, as well as notes naming each of the features on the diagram
• Scale: A map or a diagram is of course smaller than what it represents. A notation on the map might show the ratio of inches to feet, or there might be a drawing of a person, showing him/her in relation to the features in the sketch
  

  and

• Scale: As above
• Notes: Labels on each of the features
• Orientation: As above
• Title: As above

As you can see, they are similar, with BOLTS asking for a border and legend, and SNOT asking for notes. It should be noted that a BOLTS/SNOT diagram contains these elements, but is not limited to these elements. That is, a field diagram should be a faithful, detailed, and accurate rendering of the object of study. It should contain as much detail as is needed for someone to understand the area being studied. So it is probably accurate to think of a field sketch as a drawing or sketch of an area which is then labeled using the BOLTS/SNOT convention.

For the logging requirements of this cache, you will combine the two types, using all of the different labels.

Section II—Terminology

As with any profession, earth scientists make use of a particular vocabulary to communicate with each other and with the public at large. What follows are some definitions that you might find useful in completing the requirements for this Earthcache. All of these terms can be applied to some parts of the outcropping between its easternmost and western most sections. The definitions are taken from the Dictionary of Geological Terms, except where indicated by an asterisks(*), in which case they are my own.

1. Angular unconformity: An unconformity in which the bedding planes of the rocks above and below are not parallel.
2. Basalt: A dark colored extrusive igneous rock composed chiefly of calcium plagioclase and pyroxene.
3. Bedding: A characteristic of sedimentary rocks in which parallel planar surfaces separating different grain sizes or compositions indicate successive depositional surfaces that existed at the time of sedimentation.
4. Calcite: A carbonate mineral that forms deposits in sedimentary rock. Crystalline in appearance.(*)
5. Chemical weathering: The total set of all chemical reactions that act on rock exposed to water and atmosphere and so change it minerals to stable forms.
6. Chert: A sedimentary form of amorphous or extremely fine-grained silica, found in concretions and beds.
7. Contact Metamorphism: Metamorphism genetically related to the intrusion (or extrusion) of magmas and taking place in rocks at or near their contact with a body of igneous rock.
8. Cross-Bedding: Layers of rock that sit at non-parallel angles, in which layers intersect, or cross, with other layers. These intersections are the result of deposition, and not subsequent geological upheaval.(*)
9. Datum plane: An artificially established, well surveyed horizontal plane against which elevations, depths, tides, etc. are measured (for example mean sea-level, or a road).
10. Deposition: A general term for the accumulation of sediments by either physical or chemical sedimentation.
11. Elevation: The vertical height of one point on the Earth above a given datum plane, usually sea level.
12. Erosion: The wearing-away of rock and soil by natural processes and elements such as wind and water.(*)
13. Extrusive: Pertaining to igneous rocks or features formed from lava released on the Earth’s surface.
14. Facies: Distinctive rock units that form during sedimentation, and which are usually distinguished by vertical layering.(*)
15. Gabbro: A coarse-grained igneous rock, chemically equivalent to a basalt.
16. Joint: A large and relatively planar fracture in a rock across which there is no relative displacement of the two sides.
17. Lava Flood (plateau basalt): A term applied to large areas of basaltic lava presumably extruded from fissures.
18. Lineation: Any linear arrangement of features found in a rock.
19. Outcrop: And exposed section of bedrock or underlying geologic formation.(*)
20. Sandstone: A clastic sedimentary rock in which the particles are dominantly of sand size, from 0.062 mm to 2 mm in diameter.
21. Sedimentary rock: A rock formed by the accumulation and cementation of mineral grains transported by wind, water, or ice to the site of deposition or chemically precipitated at the depositional site.
22. Sedimentary structure: Any structure of a sedimentary or weakly metamorphosed rock that was formed at the time of deposition; includes bedding, cross-bedding, graded bedding, ripples, scour marks, mud-cracks.
23. Stratification: A structure of sedimentary rocks, which have recognizable parallel beds of considerable lateral extent.
24. Vein: a line of crystalized mineral formed from the presence of water. In marine sandstone these usually form within cracks. geological activity causes the cracks to re-open, which in turn causes further depositon of aqueous minerals.(*)

Section III—Geology of the Hermanus Region

Geologists classify rocks into three main types: Sedimentary, Igneous, and Metamorphic. Sedimentary rock is formed from the deposition of minerals and organic particles on the earth's surface and on the bottom of the oceans. Hermanus sits in the Western Cape of South Africa, along what is called the Cape Fold Belt. Most of the prominent rock formations are composed of either sedimentary sandstone, metamorphic shale, or igneous material.

Sedimentary rocks are formed by the layering of various materials on the surface of the earth or on the ocean floor. The materials can be organic or mineral, and the process of formation means that sedimentary rocks cover most of the earth's surface, but are underlayered by igneous and metamorphic rock. There are four types of sedimentary rocks: clastic, biochemical, chemical, and a broad category of "other" types. The category of clastic rock includes sandstone, which is common to South Africa. Sandstone is formed from the accumulation of small grains, most commonly quartz and feldspar. Sandstone can be any color, but typically follows the colors of sand found on beaches--white, grey, tan, brown, pink, or black. Sandstone forms in two stages. First, sand accumulates through sedimentation, as sand settles to the bottom of rivers, lakes, the ocean, or falls to the ground, typically in deserts. In the second stage, as deposits accumulate, the underlying layers are compacted and cemented together by the minerals in the sand. Sandstone therefore takes on the grainy texture, and while it can be used in building materials, it is gritty and easy to carve. The process of formation also means that the face of sandstone formations can have a layered appearance, oftentimes with small waves or ripples, or even mineral deposits but also, just as often, as stacked chunky layers.

Metamorphic rock is the result of the transformation of other sedimentary, igneous, or metamorphic rock through heat and/pressure over time. Metamorphic rock is usually found deep below the earth's crust, but comes to the surface through erosion or uplift due to tectonic change. Examples of metamorphic rock include coal and shale. Marble is an example of a metamorphic rock formed from sedimentary limestone.

Intrusive igneous rock is formed below the crust of the earth from magma that slowly rises to the surface of the earth, pushing through existing rock nearer the surface. As the magma cools, it absorbs minerals from the surrounding rock, giving it a coarse, grainy texture. The slow cooling of the rock also allows for the formation of large crystals, which are visible to the naked eye and give igneous rocks a shiny, shimmery character. The large grains in the center cool more slowly than the grains that come in contact with the surrounding rock. The magma generally does not form discretely visible layers the stretch over a distance, except in that the intrusive rock might create a thick horizontal layer or a vertical column between existing rock. So a common visual marker of an intrusive igneous rock is a sharp, distinctive change in color along a horizontal or vertical line that looks like a "rock sandwich" (which it is).

Extrusive igneous rocks originate in subsurface magma that reaches the surface, usually through volcanic activity. Lava flows and fragmented volcanic rocks are both extrusive, and the rapid cooling of the rock as it is quickly forced to the surface results in rocks that are glassy, like obsidian, or crystaline in structure. The texture of extrusive igneous rock can therefore be grainy or porous, or smooth and glassy. While both obsidian and pumice are a type of glass formed from lava, the composition and processes that create the two are quite different. Still the two are sometimes seen together.

Requirements for logging this cache. Read this carefully before beginning!

1. Create a detailed field sketch, as described in Section I above, of the outcropping and the unusual geological feature. Your sketch must be about 10 feet wide and 20 feet tall, and cover the area from the top to the bottom of the outcropping. The two sides of your field sketch must be clearly marked with natural boundaries that I and other visitors will easily recognize.
2. The field sketch must be annotated with a BOLTS/SNOT diagram, again as described in Section I above. Your diagram must contain all of the components of BOLTS/SNOT, using the following guidelines:
   • The field sketch should have at least ten distinct features of the section using terminology from Section II above, and drawing on the knowledge gained from Section III. Two of the labelled terms must include the unusual layers in the rock outcropping.
   • The ten features should be labeled with numbers, not with the terms.
   • The drawing should indicate the scale.
   • You must clearly sign the BOLTS/SNOT diagram with your geocaching name across some part of the drawing, without rendering the drawing unreadable.
3. Use your phone to take a photo of your diagram, or scan it using a scanner. Upload the file with your log. The photo/scan of your BOLTS/SNOT diagram must accompany your log. Logs not accompanied by a picture or scan of a BOLTS/SNOT will be deleted.
4. In an separate e-mail, answer the following:
   • List what each of the numbers represents on your diagram.
   • List the cause of the unusual layers at GZ.
   • Note the size of the crystals in both the marine sandstone and the non-sandstone unusual feature. Based on their size do you believe that they cooled quickly or more slowly?

A final note. First, please practice Cache In, Trash Out wherever you go. You don't have to haul out a Hefty 50-gallon trash bag for every cache you find, but please be conscientious about the areas in which you cache. It doesn't take a whole lot of effort to leave a caching area bit nicer than you found it—taking away one piece of trash will do it. That makes it better not just for the next cacher, but also for the muggles. To mangle a phrase: Take Out Some Trash, Leave Only a Signed Log.