DESCRIBING INACCESSIBLE OUTCROPS ALONG THE MIDDLE FORK OF THE VERMILION RIVER, ILLINOIS

Geologic features exposed in outcrop along stream banks provide valuable insight into the composition, thickness, succession of units, lateral extent, and variability of deposits composing buried landforms and depositional sequences on floodplains. These outcrops are often short-lived, disconnected, and inaccessible. Even when accessible, considerable expense, safety issues, and logistical limitations may prohibit detailed description of the site. Close-range photogrammetry and terrestrial lidar may be used to remove these obstacles and produce 3-dimensional, geo-referenced imagery for measurements of geologic features in outcrop.

Deposits of the Wisconsinan glaciation (tills of the Yorkville, Batestown and Tiskilwa Members of the Lemont Formation) and Illinoian glaciation (till of the Glasford Formation and associated meltwater sediments) are exposed at outcrops along a 3-kilometer stretch (river length) of the Middle Fork of the Vermilion River in East-Central Illinois. Stereo photography and terrestrial lidar imagery were collected at four streambank exposures to allow the incorporation of remotely-sensed outcrop information into ongoing 3-dimensional geologic mapping efforts. Features such as boulder pavements, incised channels, and structures resulting from subglacial deformation were imaged during field data collection. Measurements were made of the elevations of unit contacts, material thicknesses, and lateral extent of facies that can be represented in 3-dimensions.

Close range photogrammetry produces a 3-dimensional image which retains all of the microtopography and color contrast of an outcrop. Contacts and features can be digitized as exposed and georeferenced coordinates can be calculated to represent these surfaces. In-situ sediment samples were collected to confirm and correct the mapping completed from the stereo photography. Repeated lidar imagery will be used to quantify sediment loss due to erosion of the outcrop over time.