21ST CENTURY TECHNOLOGY APPLIED TO 19TH CENTURY MAPS: UPDATING THE LATE WISCONSIN TERMINAL MORAINE IN SOUTHEASTERN INDIANA

Leverett and Taylor (1915) is the seminal work on surficial geology of the upper Great Lakes region. Their observations about the character and spatial relationships of moraines, outwash, and other landforms still amazes. Their map remains the standard from which all subsequent maps of Michigan and Indiana are judged. We mostly add details or improve accuracy to their maps, mainly because the detailed topographic maps, soils data, and air photos we take for granted did not exist in the early 1900s. This is not to say that their work was flawless, that their interpretations are always right, or that the details we add are insignificant. Their flaws, especially a modern understanding of glacial processes, and our new details, notably new digital data sets like LiDAR, are particularly relevant to a contemporary perspective on the late Wisconsin terminal moraine in southeastern Indiana.

We used SSURGO soil data, the new Indiana statewide LiDAR, and other digital data within a GIS framework to identify details of glacial landforms and features from southern Indiana at scales and resolution not possible at the turn of the 19^th or even 20^th century. These include subtle (<2 m high x <100 m wide) morainal ridges, “push moraines”, and ice-margin fractures or crevasse fills, as well as other sub-glacial and glacial-marginal features associated with Leverett and Taylor’s inner and outer border of the Shelbyville (Terminal) Moraine and younger Champlain (Crawfordsville) and Bloomington (Knightstown) moraines. GIS allowed us to trace these very subtle ice-marginal features and related morphosequences along the ice front on large and small scales to offer a comprehensive picture of ice-margin relationships and processes.

One distinctive characteristic of the terminal moraine noted by Leverett and Taylor, and first pointed out by Chamberlain, is that little or no outwash appears to emanate from it across southeastern Indiana. Our comparatively more refined understanding of ice sheet dynamics and processes begs the question, how is this possible? What does a lack of outwash tell us about ice dynamics during the formation of the terminal moraine? When and where do ice-margin drainage systems become common during the retreat from the terminal moraine? We will discuss these and other issues using the details afforded by LiDAR and soils maps.