accretion on the neap berm is caused by erosion of sediment at the base 

 of the beach face which is then deposited at the distal end of the neap 

 high tide swash. As tides move from neap conditions toward spring con- 

 ditions, the neap berm moves up the beach face (lower diagram, Fig. 54). 



Accretion on the neap berm also occurs in the form of sediment moved 

 from the back dune region onto the beach by westerly and northwesterly 

 winds. Immediate poststorm conditions on 7 January are shown in Figure 

 55. A small neap berm had begun to form; however, the profile was gen- 

 erally featureless. As the low-pressure system moves out of the area 

 and the winds shift to the west, considerable sediment is moved onto the 

 beach by eolian transport. Coarse-grained eolian wind ripples migrating 

 across the back dune area are shown in Figure 56. Similar eolian ripples 

 are common on the backshore during the winter (Fig. 57). While sediment 

 from the dunes was deposited on the beach, small ridges were forming off- 

 shore and migrating landward. During the study period these ridges were 

 of low amplitude, and were rarely as long and continuous as the ridges 

 during the summer. Although actual measurement of ridge migration rates 

 was difficult (to qualitatively locate a ridge slip face from one low 

 tide to the next) , ridges moved more quickly across the low tide terrace 

 during early poststorm conditions than during later stages in beach 

 development (Fig. 58). 



Temperature extremes in winter caused changes in beach morphology 

 not experienced during the summer. Relatively higher winter temperature 

 for the first part of the study (in the lower fifties) caused a lowering 

 of the frost table in the back dune area. The level of the frost table 

 marks the limit to which sediment is eroded from the dune area by the 

 wind. The result of the lowered frost table was that more sediment 

 moved onto the beach from the dunes than would have been eroded had the 

 frost table been closer to the surface. A comparison of profiles from 

 25 and 26 January, after offshore winds averaged 40 miles per hour on 

 25 January (Fig. 59) , reveals up to 30 centimeters of deposition on the 

 low tide terrace. The sand deposited on the low tide terrace was deliver- 

 ed to the surf zone by the wind. The waves depositing the sand were 

 flattened out by the offshore wind which was strong enough to maintain a 

 constant tidal elevation for 3 hours preceding high tide on 26 January. 



Extreme cold which causes parts of the beach to become frozen is 

 important to erosion of the beach face and berm. Most of the water that 

 ponds on the berm at high tide percolates into the sand and when the 

 temperature is below the freezing point of saltwater it will freeze the 

 berm and sometimes the beach face. At the next flood stage of the tide 

 the frozen part of the beach face inhibits erosion. However, after a 

 break occurs in the frozen surface, the beach surface is vulnerable to 

 erosion. Erosion at the berm crest near high tide is shown in Figures 

 60 and 61. The effects of this process are generally greatest along the 

 edges of bays between beach cusps, although similar effects have been 

 noted on the high tide beach face where a frozen high tide swash may 

 also inhibit erosion. 



74 



