Lava Pillows, not for Sleeping……… EarthCache
Lava Pillows, not for Sleeping………
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This earthcache is about this unique bedrock found along the southeast coast of Grand Manan Island. When you see the rocks it becomes easy to understand the name.
As you cross the area you will notice what appears to be a somewhat different type of bedrock. These are called Lava Pillows or Pillow Lava or Pillow Basalt and were formed 200 million years ago during the Early Jurassic period. Pillow lava gets it’s name because it looks like pillows that are stacked side by side on their edge. Pillow lava is formed underwater and gets its shape because it is cooled quickly.
Pillow lava, also called lava pillows, consist of rounded lumps of lava typical of eruptions underwater, where the cold sea water quickly freezes the hot rock, shaping it into “pillows,” unlike the lava flows on land that run in long streams. The shape of pillow lava is usually spherical or elliptical. It is rounded on the topside and flat or concave at the bottom made of Basalt. Basalt is a fine-grained igneous rock that is made up of several minerals; some of them are feldspar, iron and magnesium. Basalt is generally a dark colored, hard, volcanic rock containing 45% to 54% silica rich minerals (SiO2), which results in low viscosity (resistance to flow). Basalt is erupted at temperatures between 2012 °F and 2282 °F. Basalt forms from rapidly cooling magma causing the fine grained, giving it a kind of a glassy look to it.
What happens is that lava comes up out of a vent in the earths crust and the outside starts to harden because the water is cold. The middle takes longer to harden so the magma keeps getting pushed out. Think of it like blowing up a balloon. The outside of the lava balloon keeps the hot lava inside and the balloon gets bigger and bigger until it is easier for the lava coming out of the vent to start a new pillow (balloon) right beside the first one. Sometimes a hole will break in the "balloon" at the top or on the side and the hot lava will flow out creating a new formation on top of one of the older ones.
Slow extrusion gives enough time for a thick crust to form on all sides of a pillow lobe, and prevents individual pillows from coalescing into a sheet. Internally the pillows are fed by a system of interconnected channels. Pillows are not typically hollow and tend to solidify all the way through and often have scrape marks on their sides that form during extrusion.
At the posted coordinates you will find yourself viewing ocean side bedrock that has been exposed to the action of the waves for years. You should be able to easily identify the features in the bedrock.
Remember this is an earthcache so there is no container just an earth science lesson at an amazing natural feature that needs to be protected. To log this cache, email me through my profile:
1) The name of the Earthcache and the number of people in your group.
2) Is the size of individual "pillows" all the same?
3) Use this information to guess as to why the sizes are uniform or not.
4) There are others features formed in the rock, determine the cause of these features, remember the pillows were formed under water.
In your log please take the time to describe what you find special about this location and its unique features, it is also nice to include photo so other have some idea what to expect.
Do not try to take the shortest path to this location, as you will find while it maybe short it is not quick. Use the “Red Trail” that circles the Island along the shore. It can be accessed where the road leaves the shore to the north in Deep Cove. You will see a red marker on a tree as well as markings on the road. Follow the trail to the shore, the trail crosses over rocks that can be slippery. This earthcache is best visited at low tide and remember the tide moves very quickly.
If you would like more information on the geology of the area, Greg McHone has an outstanding webpage called Grand Manan Geology at (visit link)
Additional Hints
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Treasures
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