inches (0.6 cm) on power lines. Storms producing 0.5-inch (1.3 cm) ice layers 

 were observed on about six occasions on the southwest coast and three to five 

 occasions on the northeast coast. The greatest thicknesses observed in these 

 storms were 1.75 to 1.99 inches (4 to 5 cm) on the coast and 0.75 to 0.99 

 inches (2 to 3 cm) in inland regions. Similarly, the AT&T data show about 6 

 damaging storms, one every 3 years along the coast and every 6 years inland. 



Data gathered by the U.S. Weather Bureau show that light freezing rain occurs 

 much more frequently than damaging ice storms. The mean annual number of days 

 with freezing rain ranges from 8 to 12 (U.S. Department of Commerce 1973a). 

 AT&T's 8-year study indicates that heavy ice storms may be expected on an 

 average of 1 day/year. As stated above, damaging ice storms may be expected 

 approximately every 3 years along the coast and every 6 years inland. 

 Therefore, areas that are stressed by heavy ice accumulations can expect 

 several "good" years between storms, whereas areas affected by thin ice 

 glazing must bear some losses every year, with greater damage occurring every 

 few years . 



Due to the cooler air prevalent along the coast during summer, thunderstorms 

 are less frequent throughout the coastal zone than in central Maine. Average 

 frequencies along the coast vary from 14 thunderstorm days/year at Eastport to 

 18 thunderstorm days/year at Portland [U.S. Department of Commerce, (NOAA) 

 irregular ] . Total numbers of thunderstorms for individual years may range 

 from 6 to 30. Stations along the inland boundary of the coastal zone show 

 frequencies similar to those of the nearby shoreline stations. Woodland, 

 Bangor, Augusta, and Lewiston average 14, 17, 18, and 17 days/year 

 respectively. Available thunderstorm frequency data are summarized in table 

 2-11. 



The period of greatest thunderstorm frequency covers the summer season, from 

 June through August. Since summer is also driest, fires caused by lightning 

 pose a serious threat. Associated hail damage is infrequent. 



The historical record shows few effects of tropical storms on the 

 characterization area. Portland has not recorded any. Farther up the coast, 

 however, the probability of a tropical storm or hurricane in any 1 year is 7% 

 (Lautzenheiser 1972) . Absolutely no "great hurricanes" have been recorded for 

 the coast of Maine. Tropical storms lose much of their intensity before 

 reaching coastal Maine and so are reduced to heavy rain and moderate winds, 

 such as those in a "northeaster." 



Geology 



The geological component of an ecosystem is the substrate on and in which the 

 flora and fauna exist. The subtrate consists of exposed solid bedrock or 

 unconsolidated deposits underlain by bedrock. 



To understand the function of geological processes in an ecosystem, it is 

 necessary to have a knowledge of the origin, composition, and surface 

 distribution of the different bedrock types, the nature and origin of the 

 unconsolidated deposits, and the processes and mediums that change bedrock to 

 unconsolidated sediments and that have transported them to their present 

 environments . 



2-35 



10-80 



