LIDAR BASED DIGITAL ELEVATION MODELS AS A TOOL FOR SURFICIAL GEOLOGIC MAPPING IN THE GILMANTON, NEW HAMPSHIRE AREA

LiDAR based high resolution, high accuracy elevation data is revolutionizing the way we interpret the geomorphology of glaciated landscapes. Digital Elevation Models (DEM) created from this data reveal many more features than can be seen on either the topographic maps or in the field, as the LiDAR is essentially able to remove trees from the landscape.

Newly released data from the 2012 FEMA Risk Map LiDAR: Merrimack River Watershed Project was used to create DEMs for portions of the Belmont and Gilmanton Iron Works 7.5 minute quadrangles in east central New Hampshire. The surficial geology of these quadrangles was previously mapped by Hildreth and Nelson (Belmont, 1998) and Wittkop (Gilmanton Iron Works, 2008). The 1m resolution bare earth LiDAR data was used to construct several hillshade models using ESRI ArcMap software. Multiple hillshades are required to interpret features in this area as the default hillshade orients the sun in the northwest quadrant. Illumination of the landscape in this orientation poorly defines features with a northwest-southeast orientation that is, in this case, parallel to the regional ice flow direction. Switching the sun to the northeast dramatically changes the view and reveals a strong northwest –southeast lineation created by extensive fluting of the till. The fluting is best developed to the east with a down-ice orientation of 133˚, while to the west the fluting dies out as the orientation transitions to 153˚. The high resolution DEMs also show sequences of up to 9 parallel meltwater channels formed at progressively lower elevations that clearly show the decay of a stagnant ice mass created on the lee side of the Belknap Mountains. Wittkop (2008) mapped a series of stagnation complexes in this area that have a unique topographic signature on the LiDAR imagery. The LiDAR also shows them to be much more extensive than originally mapped.

The DEMs also show a large 1.4km long landslide developed in till just south of the divide in the Belmont Quadrangle. This is an old earthflow type feature with a 600m long head scarp having approximately 50m of relief. Its irregular surface expression on the DEM gives it a unique signature that is hard to miss. The addition of high resolution LiDAR to the analysis of the geomorphology of this region offers a quantum leap in our ability to map the surficial geology.