(west) relative to its 1900 position (Fig. 15.7a). 1. Why did Assateague Island
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Question
(west) relative to its 1900 position (Fig. 15.7a). 1. Why did Assateague Island migrate landward? 2. Field inspection of the west side of Assateague Island reveals that muds of the lagoon (Sinepuxent Bay) are being covered up by the westward-advancing island. What was the rate of Assateague Island's westward migration from 1942-1964 in m/year? Show your work. 3. Based on your last answer in part B2 and extrapolating from 1964, in what approximate year would you predict that Sinepuxent Bay should cease to exist as the west side of Assateague Island moves westward? Show your work.Explanation / Answer
Assateague Island Migration
1. The Migration:
The Assateague Island is a 37-mile (60 km) long barrier island located off the eastern coast of the Delmarva peninsula facing the Atlantic Ocean. The northern two-thirds of the island is in Maryland while the southern third is in Virginia. The Maryland section contains the majority of Assateague Island National Seashore and Assateague State Park. The Virginia section contains Chincoteague National Wildlife Refuge and a one-mile stretch of land containing the lifeguarded recreational beach and interpretive facilities managed by the National Park Service (or NPS).
Assateague has changed in form over the years. The structure of barrier islands is determined by movement of sand in the littoral zone, the land-facing side of the island. At one time, the island was connected to the lowest point of Fenwick Island. However, the 1933 Chesapeake–Potomac hurricane created an inlet south of Ocean City, Maryland. This inlet separated the two landforms. Normally, it would have silted back due to the littoral drift that ran from north to south. However, after the storm, between 1933 and 1935 a permanent system of artificial jetties was built to preserve the inlet as a navigation channel. As a result, the island has drifted considerably westward, and the two landmasses are now over 0.62 miles (1.00 km) apart.
The island is moving westward as a result of sea-level rise and the force of the surf through a process called "island rollover."Sand is eroded from ocean beaches during severe storms, carried across the island by flood waters, and re-deposited in marshes along the western shore. While this moves the island westward, it brings it closer to the mainland. Strong storms can also cause inlets to be carved through the strong movement of sand, which occurred in 1933 resulting in the separation of Assateague and Ocean City. Long shore currents can eventually deposit sediments and close these gaps unless, like the Ocean City inlet, it is maintained with jetties and dredging.
2. The Migration Rate during 1942-1964:
The migration rate can be calculated by calculating the overall rate of migration from 1933 to 2011. It is estimated that it migrated 1 km or 1000m westward from its position in 1933. So it can be calculated that in 78 years of duration it moved 1000m so per year movement will be 1000/78 = 12.8205m/year. So in overall movement will be 282.0513 m in 1942 to 1964 duration.
3. Extrapolation from 1964:
It can be calculated by measuring the distance on map from 1964 edge to present Sinepuxent bay position. It came on average 2.5 cm on map. It can be calculated that 1 cm is equal to 0.272 kms. So if you calculate then to cover the distance it will take around next 56.8 year to siege it.
Calculation
1933to 2011
78 yrs
rate /year
1000/78=12.82051
1942 to 1964
22 yrs
rate /year
12.82*22=282.0513
from map
5.5 cm
1.5 km
1cm=1.5/5.5
0.2727 km
distance on map from 1964 to present
2.5 cm or 0.6818 km
movment have to cover 0.68km or 681.81 m
rate of per yr movment
12.82
so years will be
681.81/12.82 =56.818 years
Calculation
1933to 2011
78 yrs
rate /year
1000/78=12.82051
1942 to 1964
22 yrs
rate /year
12.82*22=282.0513
from map
5.5 cm
1.5 km
1cm=1.5/5.5
0.2727 km
distance on map from 1964 to present
2.5 cm or 0.6818 km
movment have to cover 0.68km or 681.81 m
rate of per yr movment
12.82
so years will be
681.81/12.82 =56.818 years
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