![]() The geologic features of the impact crater as well as the layers of sediments that now overlie the crater. Other processes key to the formation of the Chesapeake Bay, the Delmarva Peninsula and consequently Assateague Island National Seashore are sea-level fluctuations, erosion, and deposition. The impact crater was identified by USGS scientists in the late 1990s, and has helped to further understanding of the Virginia Coastal Plain as well as studying other processes related to this ancient event such as land subsidence, river diversion, disruption of coastal aquifers, and ground instability. Over the past 35 million years the crater has been filled with thousands of feet of sediment, but the crater created a depression in the landscape toward which rivers converged, which helped determine the location of the present day Chesapeake Bay. ![]() The bolide created a crater as deep as the Grand Canyon and as wide as Rhode Island. It was into this continental shelf that a 2-3-mile-wide bolide (also known as a meteoroid) collided. Much like today, a broad continental shelf lay beneath the ocean, extending east toward the edge of the coastal plain. Thirty-five million years ago, sea levels were much higher, and the coastline of present-day North America was much further to the west. The existence of the Delmarva Peninsula in its present location can be attributed to two main factors: a bolide (asteroid) impact some 35 million years ago and thousands of years of changing sea-levels and consequent sedimentation. The Delmarva Peninsula lies within the Atlantic Coastal Plain, which consists of thousands of years of sediment accumulation that has been weathered, eroded and deposited offshore of the continent. Assateague Island lies off the western coast of the Delmarva Peninsula, which separates the Chesapeake Bay from the Atlantic Ocean. ![]() To best understand the geology of Assateague National Seashore, we must first explore its larger surroundings. Formation of the Chesapeake Bay and Delmarva Peninsula
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