Volcanic Tuff near Louisbourg Lighthouse – Part 1

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Rocks composed of volcanic ash (tuff) near Louisbourg Lighthouse in Cape Breton, Nova Scotia.

The rocks around Louisbourg Lighthouse on Cape Breton Island in Nova Scotia belong to the Lighthouse Point Member of the Main-a-Dieu sequence (formerly assigned to the Fouchu Group). They were deposited 575 million years ago, following a series of explosive volcanic eruptions in a subduction zone at the edge of a continental plate. They are the youngest rocks from the Coastal Belt and represent the end of an era of violent volcanic eruptions in this part of Avalonia. The pyroclastic deposits around Louisbourg Lighthouse are made of compacted pumiceous ash in ignimbritic units, and the resulting rock is called tuff. Layers within the tuff, distinguished by varying shades of grey, represent a series of separate eruption events. The grey layers transition into a purple layer of welded tuff where the ash and debris remained hot enough to melt the individual particles together as they landed.

[We stayed at the most excellent Louisbourg Harbour Inn while we explored this part of Cape Breton Island.]

2 Replies to “Volcanic Tuff near Louisbourg Lighthouse – Part 1”

  1. Interesting info on the formation of the rocks Jessica, and great wide shots. My favourite is probably the lighthouse – always a nice addition to a landscape.


  2. People are very fond of lighthouses in Canada. Sometimes there are sign-posted Lighthouse Trails that visitors can follow in their cars. As the lighthouses all seem to look fairly similar to me, I guess what people are really interested in is the rugged view.


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