Grand Manan Lava Tube EarthCache
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Welcome to Seven Days Work and Eel Brook Beach. These rocks are from the middle member of the lava flows found on the western half of Grand Manan Island.
While the east coast of North America is generally not known for its recent volcanic activity at one time it was very active with many lava flows. Many may have never realized that lava tube can also be found on the east coast but are much older. A lava tube is a natural conduit through which lava travels beneath the surface of a lava flow, expelled by a volcano during an eruption.
Lava tubes are a type of lava cave formed when an active low-viscosity lava flow develops a continuous and hard crust, which thickens and forms a roof above the still-flowing lava stream. Tubes form in one of two ways: by the crusting over of lava channels, and from lava flows where the lava is moving under the surface. Lava usually leaves the point of eruption in channels just as water in a river. These channels tend to stay very hot as their surroundings cool. This means they slowly develop walls around them as the surrounding lava cools. These channels can get deep enough to crust over, forming an insulating tube that keeps the lava molten and serves as a conduit for the flowing lava. These types of lava tubes tend to be closer to the lava eruption point.
If it is further away from the eruption point, lava can flow in an unchanneled, fanlike manner as it leaves its source, which is usually another lava tube leading back to the eruption point. These flow areas of surface-moving lava cool, forming either a smooth or rough, ropy surface. The lava continues to flow this way until it begins to block its source. At this point, the subsurface lava is still hot enough to break out at a point, and from this point the lava begins as a new "source". Lava flows from the previous source to this breakout point as the surrounding lava of the flow cools. This forms an underground channel that becomes a lava tube.
At the posted coordinates you find yourself looking into a small lava tube. If you look inside you will see its structure and if you move away from the cliff you will see how the lava in this area moved. As you walked toward the posted coordinates you pass many smaller mineral/crystal fill tubes.
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) Describe the size of the lava tube.
3) Which type of flow do you feel caused this lava tube?
4) There are many minerals/crystal in the rock around the lava tube. Describe where these minerals are located? They are white in color.
The access this location, follow the Whistle Road for about 1.5 km where you will find a place just past the old dump. If you go past this location you will cross Eel Brook and find another trail. Just head north down a well-worn path to Eel Brook Beach. Do not try to take a shorter path because you will only run into cliffs. This earthcache is best done at low tide.
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
(Decrypt)
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Treasures
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