The Geomorphology of Hog Island, Virginia: A Mid-Atlantic Coast Barrier

Recent shoreline changes along the Virginia barrier islands indicate that these islands are the most dynamic along the mid-Atlantic coast. Hog Island, Virginia, has been rotating in a clockwise direction for the last 122 years; the shoreline has transgressed over 2.5 km along its southern shoreline and regressed over 1.5 km in the north. Prior to 1871, the island was rotating in a counter-clockwise direction. Between 1949 and 1989, high erosion rates (13 m/year) to the south and high accretion rat.es (13 m/year) to the north have led to reworking of approximately 50 percent of the island. There is, however, at least one feature on the island which is at least 300 years old.

The geomorphic history of Hog Island was deciphered by analyzing historical shoreline charts and aerial photography, juxtaposition of landforms, and the physical characteristics of the island along transects. On the modern landscape, five physiographic regions have been identified: 1) Overwash Flat and Dune Ridge; 2) Transitional; 3) Continuous Dune; 4) Overwash Fan and Terrace; and 5) Spit Complex. Sediment samples were collected from seven landform types (beach, berm, dune, overwash, relic overwash, runnel, and threshold) in each region and found to be homogeneous in mean grain size. By comparing the older landform morphologies and island configurations to the more recent island characteristics, it has been found that Hog Island has acted as a drumstick barrier throughout the history of visible landforms. It has also been found that at least three changes in the rotation of the island have occurred: 1) late 1600's; 2) middle 1700's; and 3) the most recent, around 1871.

Study of historical chart data reveals that the entire Virginia barrier chain has undergone major morphological change around 1871: Fishing Point was created as an extension of Assateague Island and Parramore and Cobb Islands switched from counter-clockwise ·to clockwise rotation. Comparison of these islands to Hog Island implies that there has been a change in a regional scale coastal agent.

The storm climate on the Eastern Shore of Virginia changed gradually from a few, continental track, storms in the late 1800's to frequent, offshore storms, in the mid-1900's, peaking in the early 1960's. These climatological variations may be affecting the mid-Atlantic coast at intervals of 100 to 120 years (peak to peak). These climatological data coincide with a change along the Virginia barrier islands in the late 1800's, a decrease in the area of Hog Island from 1871 to the 1960's, and a shift in the ebb delta position and channel southward from the late 1800's to the 1970's. By projecting the 60 year climate variation to a 120 year cycle of peak to peak (a contemporaneous maximum clockwise rotation of Hog Island), the geomorphic data are independently fitted into a climate dominated system. Maximum clockwise rotation (with intervening maximum counter-clockwise rotation) occurred in the mid to late . 1900's, early to mid 1800's, early 1700's, and around 1600.