Correct Response: D. The sediments of the Mississippi Delta are constantly compacting under their own weight. Regular input of new sediment from the Mississippi River maintained the areal extent of the delta for millennia by adding sediment to the surface. Flood control levees, changes in land use, and channelization of the lower Mississippi have substantially reduced sediment input. Without sediment input, wave action and compaction have caused the Mississippi River Delta to rapidly decrease in areal extent as it drops below the water's surface. Overuse of groundwater in the region (A) is not a major factor affecting the delta's size and the North American plate is not down warping in the region (B). Although major storms play a role in eroding the delta, they have not increased in frequency (C) and are not the primary cause of the delta's relatively rapid decrease in size.
