PERMISSION:
This earthcache was placed with permission of the Deputy Chief, Division of Interpretation & Education, Shenandoah National Park.
EARTHCACHE REQUIREMENTS:
Each cacher must send in their own answers when logging this find. After you arrive at this creation of nature, enjoy this geological feature and what you will bring home with you through this experience. Review the materials below and answer by message/email the questions to the best of your ability. Please follow all logging requirement and do not post any answers in your log. Please stay on the trail to locate the earthcache.
ABOUT LIMBERLOST TRAIL:
Parking for Limberlost Trail is located at MP 43 on Skyline Drive. Limberlost Trail is a 1.3 mile long trail for all people and all abilities. The trail's maintained surface makes it easy to negotiate and offers frequent spots with benches to sit and enjoy these beautiful surroundings. This is a designated TRACK Trail (https://www.kidsinparks.com) which also adds to the learning and enrichment of traveling this trail. Brochures with information on TRACK are located at the trailhead.
WHAT IS A COLUMNAR JOINT?
Joints are fractures or breaks in rocks. Columnar joints are a specific joint pattern. They contain aspects of structural geology and igneous petrology. Columnar joints are parallel, prismatic columns in basaltic flows and in some cases, other rocks. This specific pattern is a direct result of cooling. The columns are normally found in shallow intrusive or extrusive igneous rock, usually either basaltic, sills, dikes and lava flows. The columnar fractures result from the cooling process. Basalt cools quickly from the outside towards the center. As a result of this, shrinkage cracks form, in a hexagonal pattern. Forms can show 3 to 12 sides in more uncommon forms. The columns vary in width of a few inches to several feet in diameter. Length is generally perpendicular to the surface of the flow. The sides of the columns will commonly exhibit horizontal markings known as chisel markings. Where a column may have broken, one side may show a concave surface while the other side is convex. Another location within Shenandoah National Park with excellent columnar jointing is found at Compton Peak in the North District.
IGNEOUS ROCKS:
Igneous rocks form when hot, molten rock crystalizes and then solidifies. This melt begins deep within the Earth close to active plate boundaries then rise towards the surface. Igneous rocks are divided into two groups, extrusive and intrusive, dependent upon where the molten rock solidifies. Extrusive igneous rock is formed when magma exits then cools above or close to the surface of Earth. These are rocks that originate at erupting volcanoes and oozing fissures. The magma cools and solidifies quickly when exposed to the comparatively cooler temperatures of the Earth's atmosphere. This quicker cooling doesn't allow mineral crystals time to grow. Therefore, those rocks generally have a very fine-grained or glassy texture. Intrusive igneous rock is created when magma is trapped deep inside Earth. Large blobs of molten rock rises toward the surface of Earth. Some of this magma can "feed" volcanoes on the surface but the majority remains trapped beneath the Earth's surface. This magma that is trapped eventually cools over thousands to millions of years until it reaches a solid state. This slow cooling allows individual mineral grains an extended period of time to grow resulting in a relative large physical size. Intrusive rock has a coarse grained texture. Basalt is a dark-colored, fine grained, igneous rock that is mainly composed of plagioclase and pyroxene mineral and usually forms as an extrusive rock. Basalt underlies more of the Earth's surface than any other type of rock.
QUESTIONS TO ANSWER:
1. Do the columns have a hexagonal pattern or are they an uncommon form of 3-12 sides?
2. Columns vary in widths of a few inches to several feet in diameter. Of the two outcrops of joints, which appears to be the larger (front or rear)?
3. What is your hypothesis on why the two columnar joints arrived at their particular positions?
4. Looking at the back of the columnar jointing, you will notice a pattern that appears symetrical, especially on the right side. What do you think was the cause of this pattern?
5. Post a photo at or near the coordinates (you do not have to be in the picture unless you want to). This is your log signature.
GINGIN'S MESSAGE:
L - Listen to the sounds that surround you
I - Inspired and refreshed by the beauty of nature
M - Mesmerized by the colors of Limberlost that abound
B - Beautiful are the deer, the bears, the birds that you might see
E - Enriching our spirits, our minds and our hearts
R - Remembering that we are visitors in these beautiful woodlands
L - Leave no trace, practice and protect
O - Observe what is all around you and embrace that energy
S - Senses you have, use each to their fullest here
T - Time well spent with family, friends or alone
T - Trail that is fun and enjoyed by all ages
R - Realizing that nature's future is dependent on your behaviors while there
A - Amongst these mountains, we share that special bond, even if for a short time
I - Ingriguing formations to study and ponder
L - Lingering a while longer, appreciating this simple yet complex land filled with wonder
Congratulations to Airsax for being FTF 8-1-21