Describe the geologic evolution of the drumlin features which make up the backbo

Question

Describe the geologic evolution of the drumlin features which make up the backbone of the Boston Harbor Islands. When were they formed and what are they made of? How did these features change over time? Diagrams can be used.

2. The population of Desert Paradise (DP)—a fictitious town in the southwestern United States—has been doubling every seven years. Most of the new inhabitants are “snowbirds,” people escaping the cold winters of more northerly latitudes. There are no permanent streams or lakes anywhere near DP. In fact, the only standing water in the town occurs in the ponds of the many golf courses that have been recently built. The water in these ponds needs to be replenished almost constantly, for without added water, the contents of the ponds seep into the ground quickly, and the ponds dry up. The golf courses and yards of the suburban-style developments of DP all have lawns of green grass. DP has been growing on a flat, sediment-filled basin between two small mountain ranges. Where does the water supply of DP come from? What do you predict will happen to the water table of the area in the coming years, and what changes to the land surface will happen as a consequence? Is there a policy that you might suggest to the residents of DP that could slow the process of change?

Explanation / Answer

Boston basin is a topographic lowland underlain by sediments deposited from the end of Precambrian, Boston Harber Islands (over thirty islands) are part of Boston basin, which have formed by repeated submergence and erosion of drumlins. The islands are predominantly made up of several drumlins, asymmetrical, elongated, scattered hills, formed by erosional action of glacier. The Harbor drumlins are part of a larger drumlin field that extends throughout eastern Massachusetts comprised of over 200 drumlins and also extends at least 16 km seaward into Massachusetts Bay. Scientists believe that this drumlin topography has formed and evolved by at least two period of glaciations. A Pre – Wisconsinan and a Late Wisconsinan age Glacial drifts have been found along with the sedimentary cover. Along with glaciations, the rising sea level at that period has shaped the island topography. The basin has been partially submerged by subsequent sealevel rise. Another important feature of this drumlin topography is the formation of accretionary salients, formed by drift convergence or a lowering of long shore energy typically in the lee of islands. The salients look like cuspate spits, and also form travelling headlands. These headlands are formed when unequal drift comes from opposing long shore directions and migrates in a direction controlled either by dominant wave approach or larger long shore sediment supply. As you mentioned, desert paradise is grown on flat sediment filled basin between two mountain ranges, no permanent body of surface water is present, so the source of the water must be groundwater. The town must be built up above good permeable porous aquifer zones below. Of course in order to continue to live in such a place require good surface water bodies. As there are no lakes or streams, artificial lakes or ponds can be built. The groundwater scenario must be checked very well. The geology of the area must be studied by experts. There should be careful monitoring so that the water table does not drop sufficiently and groundwater do not get exhausted. There should be proper regulations on the use of the water sources available.

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