Table 3.

The main high-volume, deep-seated landslides affecting the road and known to the authors

Chainage (location)DateLandslide typeGeologySurface area (m2)Depth (m)Volume (Mm3)Remarks
266 + 900Pre-1997Rock slideMetavolcanic rocks, principally andesite, destructured and often faulted with adverse jointing in most locations15 000150.15Stabilized–dormant
267 + 750Oct. 200931 000150.33Stabilized–dormant
282 + 700Pre-199740 000300.83Dormant
300 + 7502004Rock–debris slide15 000150.14Reactivated
300 + 900 (Sayangan)200412 000150.12Reactivated
314 + 100Pre-1997Wedge11 000150.10Dormant
317 + 500 (Sinipsip)Pre-1997Rock slide68 000301.50Active
318 + 000Pre-1997, reactivated 2018Rock slide114 000503.70Active
318 + 900Pre-1997, reactivated 2018Rock slide256 0006011.00Active
323 + 000 (Pilando)Pre-1990Rock slideVolcaniclastic rocks, tuffaceous siltstone and mudstone, adversely dipping170 000604.30Active

‘Volume’ refers to the volume of ground displaced by the landslide and is based on the expression 1/6πDWL (Working Party on World Landslide Inventory 1990). Some of these landslides have had significant volumes already ‘evacuated’ from the source areas. Surface areas and especially volumes are very approximate and largely indicative.