Boston Harbor and its islands
http://www.nps.gov/boha/pphtml/subnaturalfeatures14.html; www.bostonislands.org
Boston Harbor (500 square miles) is an estuary system where the salt water of
Massachusetts Bay mixes with fresh water from three rivers: the Charles, the Mystic, and
the Neponset. Geological formation of the Boston harbor and its today’s 34 islands
started about 100,000 years ago. At that time two separate periods of Pleistocene
glaciation formed the hills that cap most islands and created the local drainage system,
consisting of the Charles, Mystic, and Neponset watersheds (see Fig 1.). The cores of
many harbor islands are drumlins-glacier-formed, asymmetrical, elongate masses of till
formed into smooth-sloped hills on the Boston Basin lowlands. In profile, they look like
upside-down teaspoons. As the climate warmed and the glacier receded from the Boston
area some 15,000 years ago, the melting of glacial ice raised the level of the ocean,
eventually creating this section of the basin and isolating the islands.
Figure 1. is based on Knebel & Circé, 1995, Seafloor Environments within the Boston
Harbor - Massachusetts Bay Sedimentary System: A Regional Synthesis; Journal of
Coastal Research; vol. 11, no. 1 http://woodshole.er.usgs.gov/project-pages/coastenviro/boseco/zones.htm
Ecosystem zones:
Watershed: area drained by rivers and streams discharging to an estuary
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rivers have been used for transportation, water supply, and waste discharge
rivers are a source of fine-grained sediments (e.g. natural sediment support for
beaches)
Estuary: a coastal embayment or the mouth of a river (e.g. Charles, Neponset, Mystic)
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characterized by mixtures of fresh and salty waters
influenced by flow of ocean tides (here ~ 10.33 feets)
protected from large waves – ‘natural buffers’ for coastal areas
tends to receive large amounts of nutrients and have high organic productivity
estuarine and marine intertidal wetlands the most common in Boston Harbor area
Inner Shelf: an area affected by tidal and storm waves and currents
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sediment erosion and redistribution by sub-aerial process during past sea-level
changes
supply of fine-grained sediments is small
Basin: deeper-water offshore area extending below normal regions of tidal- and storm-induced
currents
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natural settling area, weak bottom currents
significant supply of fine-grained sediments, with much lower organic matter
than in estuaries
What is a drumlin?
A drumlin (Gaelic druim the crest of a hill) is an elongated whale-shaped hill formed by
glacial action. Its long axis is parallel with the movement of the ice, with the blunter end
facing into the glacial movement. Drumlins may be more than 150 ft (45 m) high and
more than 1/2 miles (0.8 km) long, and are often in drumlin fields of similarly shaped,
sized and oriented hills.
There are many theories as to the exact mode of origin and plenty of controversy among
geologists interested in geomorphology. Some consider them a direct formation of the
ice, while a theory proposed since the 1980s by John Shaw and others postulates creation
by a catastrophic flooding release of highly pressurized water flowing underneath the
glacial ice. Either way, they are thought to be a waveform (similar to ripples of sand at
the bottom of a stream). It is also poorly understood why drumlins form in some glaciated
areas and not in others.
Drumlins may occur as scattered single hills, or in so-called "swarms." The Boston
Harbor Islands are a geological rarity, part of the only drumlin swarm in the United States
that intersects a coastline (Fig. 2). This "drowned" cluster of about 34 of more than 200
drumlins in the Boston Basin are not all elongate in shape, as most other drumlins are
(molded in the direction of glacial flow). Geologists believe the islands illustrate two
separate periods of glacial action. Many of the islands have more than one drumlin.
Figure 2. Boston Harbor http://www.nps.gov/boha/parkmaps/map_boha.pdf
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Figure 3. Deer Island Waster Water Treatment
http://www.nps.gov/boha/pphtml/subenvironmentalfactors22.html
Today, Boston Harbor is much cleaner than it has been for decades, as in most developed coastal
areas, the harbor had been used for waste disposal since colonial times. Sewage from 43
municipalities now undergoes state-of-the-art primary and secondary treatment at Deer Island
(Fig. 3.). Sludge is removed and the effluent is disinfected and dechlorinated, ready to be
discharged through a 9.5-mile outfall tunnel. The effluent is mixed with the deep waters of
Massachusetts Bay (see Fig.1.).
Boston’s historic ‘coastal management’ – the original Shawmut peninsula
http://www.iboston.org/rg/backbayImap.htm
1630
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Defined by three mountains: Fort Hill, Copps Hill, and Trimont
Easy to defend from land and sea attack
Total land mass: 487 acres
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1830
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Mill Pond adds 10% more land to Boston Proper
New State House occupies top of reduced Beacon Hill
Pemberton Square / Scollay Square created.
1845
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Great Cove created much of Boston's Financial District
South Cove is today the China Town & N.E. Medical Center
Combined, they added 60% to Boston's original land area.
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1865
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Added land along Charles St. and West End
Created ropeworks on west end of Commons
Expanded Boston's original land mass by 40%.
1890
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The most convenient fill from Boston's hills was already used
Fill was transported from Needham Heights. <more info.>
Added more land than the entire Shawmut peninsula
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