Sumatran Fault roadcut

3D Model

Northwest of the village of Sipirok in Sumatra, a huge roadcut has been excavated through a compressional section of the Sumatran Fault. Within this roadcut, the primary fault strand juxtaposes pumice-rich lake deposits with thick welded and non-welded tuffs. The northeast part of the roadcut shows how faults that appear to have normal displacement occur within a large anticlinal fold - in fact, most of these faults are strike-slip! Radiometric dating reveals that the folding has taken place since ~350,000 years ago (the eruption age of the thick welded tuff). Look for charcoal beneath ash layers (ex-jungle!), carbon-rich beds within the lake section, non-welded tuff (smooth white areas) and welded tuff (blocky gray areas). The main fault strand separates the tuffs from the yellow, well bedded lake deposits. Quite a complex outcrop for a ‘simple’ strike-slip fault.