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Cape Cod Volcanoes in Massachusetts?

Whoever heard of a red-hot volcano in Massachusetts? You would have hard work to find one; in fact, you could not find one today. Yet, we are told by geologists that once upon a time active volcanoes poured out black and red felsites, (which were dense, igneous fire-made rocks consisting of feldspar and quartz) under the sea in Nantasket, Hingham, and Mattapan, Boston.

That was when the famous granites of Quincy and other places on the South Shore welled up from below, and through the interstices or spaces between these came the molten traprock, which was fine-grained, colored, igneous rock in somewhat columnar shape. You can see some of this traprock in the greenish ledges of Cohasset today.

There were so many of these volcanic eruptions, as well as violent earthquakes, that the disgorged materials covered the bottom of Boston’s water basin with varied patterns of deposits. Eventually, as we realize, the submarine disturbances quieted down and ceased.

At that time also, the edge of the entire continent along our shoreline was lifted up higher than it is now. You would therefore have had to walk some distance to reach the ocean shore, for it was farther east than at present. All the gravel-formed hills of today were missing, and the ponds and small lakes that we now find everywhere here, simply did not exist.

Blue Hill, just southwest of Quincy, would be perhaps the only place which we of today would recognize if we were whisked by magic back into that distant era. The ancient river, which in those days had for its mouth the area which we call Massachusetts Bay, emptied into the sea somewhere beyond Provincetown. There, deep in the ocean bottom, six hundred or more feet down, still lie the grooves or canyons through which this vast river for ages cut its way oceanward. By then, even the fiery volcanoes which had spewed their molten contents into the Bay, were quenched and dead.

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Cape Cod
Posted by Cape Cod - (website) on 06/03/06
Categories: NatureOff Cape
Keywords: geology, nature, off cape



Posted by Carol Noel on 03/18/11 at 03:13 PM | #

Hello. I have studied this topic for 30 years, and am considering publishing a book at some point, containing all of my notes and research. My focus will be on showing where the centers of many of the ancient Eastern MA volcanoes are located now. There was a fairly good amount of study and writing done on this topic in the 1800’s, but interest seems to have died off, as opposed (for an example) to the current interest in Canada, where the research is non-stop, and the list of Canadian volcanoes (including necks/plugs in Eastern Canada) on Wikipedia is truly extensive. Based upon my reading, and also personal studies made of old lava flows (in the Newbury/Ipswich/Essex/Rowley area, as well as the Marblehead/Beverly/Salem area, and finally the Malden/Revere area) and such (and some studying done with some help from the MA state geologist), I’ve been able to locate the centers of many of the “old volcanoes”, which (in most areas) would be recognized and referred to as volcanic plugs, necks, pipes, diatremes, maars, ring-dikes or calderas. Here in MA, and quite possibly due to the major erosion of said volcanoes (due to the extreme summer humidity, cycling with the cold dry winters), plus much heavy vegetation overgrowth, not to mention destruction of some of the centers by quarrying and/or building…there doesn’t seem to be much research or even interest in locating the old volcanoes or their remnants. Old works by the likes of Hitchcock, Sears, Clapp, Price, et al have proven quite helpful in studying an area of research which has proven itself to be (apparently) somewhat archaic and/or orphaned. If you need more info, feel free to contact me at:

Posted by Mark Smith from Massachusetts, USA on 04/14/11 at 01:35 PM | #

I found a volcanic rock on a beach in cape cod today, in Brewster, Wing Island.  Where did these rock come from, was just sticking out the sand yards from the beach.

Posted by mike from Brewster, Ma on 06/04/11 at 02:21 AM | #

Funny-I just found a Geode on the beach in
Provencetown. I can only assume it was brought here by a glacier from some old volcano up north since the cape is made up of rocks brought here from the north.

Posted by Tom DiCesare from Yarmouth on 06/10/11 at 03:32 PM | #

I recently found some black obsidian stones in a Mattapoisett woods.  I first thought there were a hard coal but the feel was wrong.  They have a slippery surface, extremely hard with inclusions of white spots.  They also have an underlying gold/amber number of spots.  The area also contain iron chunks.  Would this be a possible indication of volcanoic activity at one time?  Can obsidian of this nature be made in a outdoor furnice?

Posted by Jan from Homw on 07/25/12 at 10:49 PM | #

I also found such a rock in Eastham. It is not obsidian, but a rock that is more common in non volcanic areas. It is called chert. It was used by the natives to make spear heads, arrow heads and cutting tools.

Posted by Tom from Eastham MA on 02/25/14 at 02:52 AM | #

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