Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The southern Andes have been eroded by the Patagonian ice sheet and are much lower and narrower (Garzione et al. 2008; Hoorn et al. 2010; Lavina & Fauth 2011).
Category: