Fire and Ice: Boston Harbor Geology 10/18/20

[Joseph Berkovitz]

People: Joe Berkovitz, Bob Levine, Brian MacCormack, Nancy Hill, Jane Cobb, Dana Sigall, Pat Donohue, Pablo DeTorres, Dan Foster, Shari Gallant

Launch: 0955; Land: 1530
Distance: 12 nm
Conditions: flat calm -> ESE 10 kt, partial sun, air 56 F water 58 F, light wind waves 1 ft
Tides at Boston Light:
6:36 AM    low    -1.13 ft
12:50 PM    high    11.66 ft
7:09 PM    low    -1.81 ft

This twice-rescheduled version of the trip finally took place today in near perfect weather and sea conditions. There were a few issues, some expected and some not. The 8-day delay flipped the tide cycle on us, so we were (as predicted) fighting some current on the way out at near max flood. Also, the Coast Guard had mistakenly told us to call them the morning of the trip to get permission to land on Little Brewster, but it turns out that the National Park Service has to approve this and they need more lead time. So we had to leave that off the itinerary—which given the current situation, was maybe not such a bad thing.

About the trip, though. We got to see some great geology on Lovells, Great Brewster and Calf Islands, and with the high water midday we were able to get very close to a lot of the coastal features, which is harder with the optimal tide cycle providing low water.

Hopefully we will get to do this again next year with folks who could not go this time.

Here are some pictures.

Lovells Island:

Boundary between argillite bedrock (below) and diabase sill (above) on Calf Island:

On the way back at Deer Island:

Edited October 19, 2020 by Joseph Berkovitz

[Dan Foster]

This was a great trip and learning experience. I look foward to all the future NSPN incident reports that start with "I was contemplating a diabase sill when the sleeper wave lifted me into the argillite..."

Thanks Joe and Bob for all the planning and preparation that went into this trip. Viva Avalonia!

[Joseph Berkovitz]

For an update on access to Little Brewster/Boston Light, please read:

 

[rylevine]

Attached is a trip report with information on Boston Harbor geology. It was a great paddle. Thanks to all the participants!

Bob

Trip report 10_18_2020 Boston Harbor Geology Paddle_ final.pdf

[Inverseyourself]

On 10/19/2020 at 1:20 PM, Dan Foster said:

I look forward to all the future NSPN incident reports that start with "I was contemplating a diabase sill when the sleeper wave lifted me into the argillite..."

Personally, I prefer the term plutonic gabbro (but I may be misinformed)