ME - Cape Neddick Geology (and a lighthouse too!)
-
Difficulty:
-
-
Terrain:
-
Size: 
(not chosen)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
This is an earthcache, which is a type of virtual. That means there is no container. Read the description and complete the logging requirements listed at the top of the description. For more on earthcaching visit www.earthcache.org.
This earthcache is located in a city park at the scenic Nubble Lighthouse.
The Terrain rating is accurate, significant rock scrambling is required. This is NOT handicap accessible.
Logging Requirements:
Send the answers to #1-#3 to me through my geocaching profile. DO NOT post the answers to any logging requirements on this site. v 1. List the name “GC3VYNW Cape Neddick Geology (and a lighthouse too!) EC Earthcache” in the first line of your email. Also, list the number of people in your group.
2. Location 1: After reading the description about Gabbro Exposure Layers determine A) which type or types of layers are present at this location. You should plan on keeping your eyes open for these layers as you scramble from published cords to location 2. B) where do you see the largest crystals within each type of formation identified?
3. Location 2 (Bubbles): A) Identify the average size of the “bubbles.” B) Also identify the tidal zone they occur in (covered nearly all the time, high tide zone; splash zone, etc. – C) how did you determine which tide zone?
4. (Completely Optional) Post a picture of yourself and/or your GPS with your log that show Nubble Lighthouse in the background. DO NOT show any of the pertinent logging information in the background.
I will only respond if you have incomplete logging requirements. Go ahead and log your cache find
GABBRO FORMATION: Most of the layered rocks of Coastal Maine are classified into groups or sequences of formations. To the untrained eyes (and to may trained eyes) it is hard to tell which rocks belong to each formation, largely because there are few fossils to help with categorizing. Fortunately, there are a few intrusions, and these intrusions often help date a formation.
Cape Neddick is unique in southern Maine, and in fact the rock you will be exploring here is considered the YOUNGEST rock in the whole state! This gabbro is considered a “pluton” because it sticks out through another rock formation and is exposed here at this neck. It was “pushed up and out” from the earths volcanic core AFTER the surrounding rock formations had formed, hence the proposition that the Cape is one of the youngest exposed rocks in the state of Maine!
“The nearly circular mass of dark gabbro in the Cape Neddick pluton …is dated in the middle of the Cretaceous period. The gabbro is layered as though it were a sedimentary rock, and in a sense, it is” (Roadside Geology Maine). GABBRO DEFINITION: Gabbro is an igneous rock composed of the same minerals that exist in the “ordinary” basalt rock that you see in a wide variety of locations worldwide. The difference is WHERE it is formed (below the surface) and thus the differing look of the crystals and “layers” present here.
TYPES OF GABBRO EXPOSURE LAYERS: In many gabbro exposures, thin layers of slightly different colored gabbro demonstrate different types of mineral present in the rock…green olivine, black pyroxine, and many others, in different concentrations. In addition, because it is a gabbro, sometimes the layers are PARALLEL LAYERS (like a stack of paper) and at other times are PERPENDICULAR (like columns) in other places one might see CURRENT-LIKE LAYERING (like waves “frozen” into rock), and in still other instances SWIRLED LAYERS (like caramel candy).
WHY IS GABBRO LAYERED? The question of course is, why is gabbro (an igneous rock) “like this” with so many characteristics of sedimentary deposition? The truth is, that geo-scientists have debated over this for years; currently most believe that it is caused by the olivine, pyroxene, and feldspar crystals beginning to form while the magma is still hot and “sticky”. And, depending upon how molten the magma was, would affect how many of the crystals could settle through the magma to the bottom of the chamber. This settling of the crystals within the magma would give the appearance of sedimentary deposits, and molten magma chambers seem to have “currents” at least at times. That is all to say that the temperature of the molten magma when the crystals are forming seems to vary quite a bit from that of granite, where the crystals form “in place”, likely because the molten magma is too thick for the individual crystals to settle.
For the rock hounds to note, when Gabbro is polished it is often called “black granite” or “labradorite.” Because of its “layers” it is considered to have a “grain” and thus lapidary specialists are careful to cut it in a cinsistent direction to allow the highest polish and darkest shine. One of the most famous gabbro displays is the Vietnam Memorial “The Wall” in Washington D.C. which is composed of gabbro from India.vv TIDAL ZONES: Depending on the tide, you will be able to scramble much further out than the GZ (the GZ cords are above the highest high tide mark, (above the spray zone).v While we could do a complete geological study about Vertical Tidal Zones, and their effect on erosion of the gabbro rocks at GZ, that is not the main point of this earthcache, but rather only a secondary one. Let’s just say that you’ll be scrambling through several tidal zones – The zones are the spray zone, high tide zone, middle tide zone, and low tide zone. Below these is the sub-tide zone, which is always underwater.
Spray Zone: This area is dry much of the time, but is sprayed with salt water during high tides. It is only flooded during storms and extremely high tides
High Tide Zone: This area is flooded only during high tide.
Middle Tide Zone: This turbulent area is covered and uncovered twice a day with salt water from the tides.
Low Tide Zone: This area is usually under water - it is only exposed when the tide is unusually low.
EROSION IN THE TIDAL ZONES: Erosion differs in each of these zones The splay zone often experiences the greatest observable level of erosion because it is most influenced by violent tidal occurances, floods, hurricanes, and the strongest of tides. Any softer or weaker rocks are eroded out of the matrix at a faster rate and sometimes unique shapes or crystals are exposed as a result
High tide zone erosion often appears to look the same as the spray zone but has a more consistent pattern of erosion along the high tide line.
Middle tide zone is a violent area and non-discriminant erosion area. Rocks are tumbled and churned in this zone. Rocks broken loose in higher zones are turned into smooth sand in this and the Low tide zone.
Resources:
Caldwell, Dabney W. Roadside Geology of Maine. Missoula, Mont: Mountain Press Pub. Co, 1998. Print.
"Intertidal Zone.” EnchantedLearning.com. N.p., n.d. Web. 13 Sept. 2012.
"White Mountain Magma Series Lab Illustrations." Union College Geology Department. N.p., n.d. Web. 13 Sept. 2012. .
Additional Hints
(No hints available.)