23.5 Dicker son: Baguio Plateau 429 



FAULTING AND LANDSLIDES IN THE BAGUIO FORMATION 



The tuff members of the Baguio formation in and around 

 Baguio do not exhibit any regularity in dip and strike, but 

 vary greatly from place to place. These variations suggest 

 many local minor faults, in addition to the well-marked contact 

 faults mentioned above. These minor faults may be due in 

 part to local slumping after the limestone beneath the Baguio 

 formation had become cavernous. Doctor Smith has advanced 

 the same hypothesis to account for the Hospital Hill slides. His 

 statement, in litt., is as follows: 



head of Bued River Canon is marked 



very interesting 



producing some rather pronounced changes 



landslides, which 1 



in the topography of that region but have also become'of first importance 



since some Government public buildings have been endangered. 



Just before one reaches the Baguio Plateau proper traveling along the 

 Benguet Road, one climbs to a bench that is largely due to subsidence 

 of material from the valley sides. There is a broad amphitheaterlike 

 area here 2 or 3 miles in length and a mile or so wide which remarkably 

 simulates the cirquelike heads of glaciated streams. At the upper end of 

 this valley there is a huge crack or series of cracks which run around these 

 hills about as the "bergschrund" found at the head of glacial cirques 

 does. On the west side of the Benguet Road the greatest slip can be easily 

 studied. There is a fault here in loose tuff, sinter, and volcanic breccia 

 amounting to at least 50 meters. The slip plane has an angle of from 

 55° to 60° and at this point trends north and south. In January, 

 1915, Mr. V. E. Lednicky, formerly of the Bureau of Science, was called 

 upon to report upon the Hospital Hill slide. The writer visited this region 

 during several seasons previous to that time, and during one of these visits, 

 in the spring of 1914, he measured the subsidence, which then amounted to 

 35 feet, and the rate of movement, which at that time was 1 inch an hour. 

 As this material is all very loose and only held together by clay, it is 

 absolutely certain that there will be other slides behind the present one 

 and the hospital buildings, unless moved, will ultimately be wrecked. 

 [Plate 8, fig. 2.] 



This subsidence is due to several factors. Undoubtedly the saturation 

 of these loose materials with water and the high angle of the valley walls, 

 which are far above the angle of repose, are important causes, but the 

 ultimate cause probably is the solution of limestones at the bottom of 

 Bued River Canon, notably at the foot of the Zigzag, which would permit of 

 the leaching out of the rocks and thereby cause the slumping of the 

 material from above. 



Similar and even greater slides occur much farther north in the Moun- 

 tain Province. A notable one at Sagada extends over even a larger area, 

 where the amount of subsidence in 1914 amounted to over 30 feet. The 

 fault crack, following the periphery of the valley head, was when seen 

 hy the writer at least 2 miles long and a large Igorot village was 

 gradually settling into the canon without any particular disturbance 

 of the inhabitants. Some time previously the Catholic church which 



