Final answer:
The irregular shoreline of Chesapeake Bay resulted from stream erosion followed by a rise in sea level. This geological process, combined with ecological challenges stemming from nutrient runoff, defines the current state of the bay.
Step-by-step explanation:
The irregular shoreline of Chesapeake Bay has been shaped by a combination of geological processes and human activities. Contrary to options such as deposition, faulting, or glacial erosion, the correct answer to what caused the irregular shoreline is stream erosion followed by a rise in sea level.
Over time, rising sea levels have led to what geologists call a transgression, whereby sediment layers are deposited progressively towards the inland as sea levels rise, which can be identified through the examination of sediment cores showing onlapping patterns.
This alteration of the shoreline is further compounded by the runoff of nitrates and phosphates from various sources including agricultural lands, urban areas, gardens, and over 150 rivers and streams, contributing to ecological issues in the bay such as dead zones. These factors, in conjunction with the natural evolution of the bay over time, have led to the current state of Chesapeake Bay, necessitating restoration efforts like oyster reef projects by groups such as the Army Corps of Engineers.