TILL FABRIC ANALYSIS AND ORIGIN OF PORTAGE GLACIER LITTLE ICE AGE MORAINES, SOUTH-CENTRAL ALASKA

Observations of geomorphic and sedimentary processes occurring in modern glaciers allows interpretations of the genesis of older glacial deposits and landforms, and has led glacial geomorphologists to place a greater emphasis on studies of glacial sedimentology. This research investigates the genesis of Little Ice Age (LIA) moraines present in Portage Glacier Valley, south-central Alaska using till fabric and grain size analysis. The present-day moraine morphology and sedimentology in Portage Glacier Valley reveals the presence of two types of till and moraines. The clast-rich medium to coarse sandy diamicton present in the AD 1852 moraine is interpreted to be a lodgment till indicating that this feature is primarily a Type A push moraine representing glacial advance of Portage Glacier prior to AD 1852. The clast-rich coarse to very coarse sandy diamicton present in the AD 1900 and AD 1922 moraines is interpreted to be a supraglacial melt-out till (ablation till) indicating that these features are ablation moraines representing glacier recession and moraine building of Portage Glacier in AD 1900 and AD 1922.