Hidden Earth 2024

The Mulu caves just keep on getting bigger… Biogenic subaerial dissolution by nitrification in the Caves of Gunung Mulu National Park, Borneo.

30 minute Lecture|Andy Farrant

Abstract

The Gunung Mulu National Park is well known for its spectacular caves including the >250 km long Clearwater Cave system. Recent expeditions have identified many unusual geomorphological features in the caves that don’t fit with traditional views of cave development. They suggest that the caves may continue to enlarge even after abandonment by the formative rivers. These unusual passage morphologies include enormous ceiling scallops, corroded speleothems, areas of spongework, corrosion residues and alteration crusts.

We suggest these are due to secondary sub-aerial biogenic dissolution. We propose that microbial metabolism within the nitrogen-rich bird and bat guano found in the caves may be responsible for this secondary dissolution. This biogenic activity significantly alters cave passage geomorphology in tropical caves and has implications for how we interpret cave passages. This talk will examine the evidence for this biogenic dissolution and suggest a novel mechanism for speleogenesis based on ammonia nitrification.