REMOTE SENSING OF COASTAL GEOMORPHIC CHANGES AFFECTED BY HISTORIC COPPER MINING AT GRAND TRAVERSE BAY, MI USING TEMPORAL LIDAR, MSS, AND AERIAL PHOTOGRAPHS

Light Detection and Ranging (LiDAR) data from four different years (2008, 2010, 2011, 2013), MSS data (Landsat), and historical aerial photographs from 1938-2013, were used to map changes in coastal morphology. The changes are due to migrating stamp sand (copper mine tailings) that were dumped into the shore zone of Lake Superior at Gay, Michigan. From 1900-1932 the Wolverine and Mohawk stamp mills dumped about 23 million metric tons (Mt) of crushed residual ore (basalt and conglomerate). The stamp sand consists of coarse sand and fine gravel-sized particles (about 85-90%), and slime clay (silt and clay, about 10-15%). Since the operations ended, littoral drift has been transporting the material southward along the beach to Grand Traverse Bay, and into offshore regions. The migrating tailings are adversely affecting fish spawning habitat in the Lake, access to the harbor at Traverse River, and recreational properties along the beach. The coarse fraction of stamp sand progressed southward along the beach to the Traverse River breakwall, where migration is halted. Of the original 23Mt in the pile at Gay, MI, about 7Mt remains on the shore south of the original pile, with the remainder (silt and clay fractions) winnowed offshore (about 12Mt). The displaced stamp sand far exceeds the volume remaining on the original pile (<4Mt).

Significant changes in beach width all along the 8km of beach were mapped in the aerial photographs, and record the progression of stamp sand southward along the beach over 8 decades. The original quartz beach sand (approximately 2-5m wide at the beach, and 1% slope in the shore zone) was gradually covered by the stamp sand, and beach widths now exceed 100m in most places and are now 3-5m thick along the entire 8km of affected area. Widths increased as much as 3m/year as measured in several transects. Vertical beach profiles from LiDAR data reveal a much steeper beach face than the original beach. Breakers have changed from spilling to surging types due to the narrower and steeper nearshore zone and beach face, as a result of the aggradation. Spits, barrier bars that now restrict water in ponds, and en-echelon offshore bars have developed rapidly over the years of longshore transport as the sand is transported southward. From analyses of the three types of spatial data, future geomorphic changes are predicted.