#The flume gorge torrent#

Basalt is from a melt that cooled very rapidly- in other words, on the surface of the earth or in the ocean. Diabase and gabbro have the same general mineral composition as basalt, but they have a larger grain size.īasalt is identical to diabase and gabbro, but is very fine-grained. The grain size of diabase is on the smaller side.

#The flume gorge torrent#

Erosion is still occurring (modified from ).Ī “flume” is a geological feature formed when a plug of basalt is worn away from between two walls of harder granite-the result is a torrent of water in a steep gorge.ĭiabase is actually a variety of gabbro which consists mainly of labradorite feldspar, augite, magnetite, and olivine.

As you walk through the Flume, look at the floor of the Gorge and you many notice remnants of the main basalt dike, and on the walls of the gorge, small trees are growing. The highly fractured granite and basalt have been eroded by frost action as well as by the brook’s water. After the Ice Age, Flume Brook began to flow through the valley again. It partially filled the valley with glacial debris and removed soil and weathered rock from the vicinity. The gorge was covered by glaciers during the Ice Age, but the ice sheet did not greatly change the surface. The basalt dikes eroded faster than the surrounding Conway granite, creating a deepening valley where the gorge is now. As the overlying rock was worn away, pressure was relieved and horizontal cracks developed, allowing water to get into the rock layers. Had this material ever reached the surface, it would have become lava flows.Įrosion gradually exposed the dikes. Because of this quick cooling, the basalt is a fine- grained rock. The basalt crystallized quickly against the relatively cold granite.

The basalt came from deep within the earth as a fluid material, and because of pressure, was able to force the Conway granite aside. Sometime after the fractures were formed, small dikes of basalt were forced up along the fractures. As it cooled, the granite was broken by closely spaced vertical fractures which lay nearly parallel in a northeasterly direction. Nearly 200 million years ago in Jurassic times, the Conway granite that forms the walls of the Flume was deeply buried molten rock. The walls of Conway granite rise to a height of 70 to 90 feet and are 12 to 20 feet apart. The Flume is a natural gorge extending 800 feet at the base of Mount Liberty in Franconia State Park, on I-93 in New Hampshire.