Boston Harbor Cruise October 15, 2007
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/coast-enviro/boseco/zones.htm
Ecosystem zones:
Watershed: area drained by rivers and streams discharging to an estuary
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Boston Harbor Cruise October 15, 2007
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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
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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Boston Harbor Cruise
Figure 3. Deer Island Waster Water Treatment http://www.nps.gov/boha/pphtml/subenvironmentalfactors22.html
October 15, 2007
Today, Boston Harbor is much cleaner than it had 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.).
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