Take out just one definite article and your post could be described as true; misleading but true.
Geothermal activity does cause some basal melting of the West Antarctic Ice Shelf but it is not THE cause of melting. Most melting occurs at the interface between relatively warm seawater and the ice shelf. The contribution of high geothermal activity in this area appears to be enhancing the movement of the ice sheet.
Here are a few links. the first is a somewhat meandering rebuttal of denier claims relating to the process. The second is an article on the research itself. The third is an abstract from one of the research papers.
