SPOT REPORT ON THE LANDSLIDE INCIDENT IN

BRGY. MARAYAG, LUPON, DAVAO ORIENTAL

In the first week of January 2014, a Low Pressure Area (LPA) brought torrential rains for several days

in different parts of the region particularly in the provinces of Davao del Norte, Compostela Valley and

Davao Oriental causing widespread flooding and several landslides. Based on the Situation Update of

the Office of Civil Defense XI dated January 14, 2014, 13 were reported as casualties while 7 are still

missing from different areas in the region. Among the fatalities/missing, 3 are from Brgy. Marayag,

Lupon, Davao Oriental.

Brgy. Marayag with geographic coordinates of 126°9'41.789" east longitude and 7°9'21.292" north

latitude is located about 33 kilometers (linear distance) northeast from Lupon proper and can be

reached via the unpaved Mati-Maragusan road. The assessed site is characterized by flat to

undulating terrain flanked by steep slopes and mountainous terrain which is underlain by poorly

indurated and highly weathered diorite to the east and metamorphosed sedimentary rocks to the west

(ABS & CAA, July 1982) while the flat central portion is underlain by Recent alluvial deposits. The

eastern side is part of the Katian Mountain Range with the highest elevation of 1640 masl and to the

west is part of the Tagopo Mountains with its peak at 920 meters.

The area is mainly drained by Sumlog River and its several tributaries characterized by

angular/rectangular drainage system cutting through steeply incised valleys. This type of drainage

pattern is a result of the structural control joints or faults in the bedrock. Sumlog river generally trends

in a NNW-SSE direction in the upper reaches or headwaters and shifts to a NE-SW direction from

Barangay Don Mariano Marcos as it exits towards Lupon and eventually drop is loads to Cuabo Bay.

Based on previous reports (NBA and RTV, Sept 2006), the assessed site as well as the adjacent

Brgy. Calapagan is believed to be a pull-apart basin developed due to the movement of the left-lateral

strike slip fault within the Philippine Fault Zone. The main fault identified as Bitanagan Fault (ABS &

CAA, July 1982) generally trends NNW and passes along the break-in-slope defining the gently

undulating terrain and the mountainous area.

As per interview, the landslide which is a characteristic of a debris flow type of mass wasting occurred

on January 12, 2014 at around 4:00 am. Although several debris flows were noted along the road on

the way to Marayag, the area that was severely affected is Po. Madasigon (proper) of Brgy. Marayag

damaging several infrastructure and houses including the barangay hall and covered court. During the

assessment, it was noted that the debris flow shifted westward towards the barangay hall and houses

as the original channel was already filled up by debris deposit. An estimate of 1 to 2-meters thick of

debris deposit composed of sand to cobble to boulder-size rocks and uprooted trees and logs covered

the area. Most of the gullies in the purok and in the vicinities served as the channel way of the debris

flow.

According to the locals, the occurrence of this type of natural hazard in the area is common. They

added that similar debris flow but in a smaller scale happened in 1976 (?), 1986 (?) and in 1993 (?).

Based on the information given, a 10-year flood/debris flow affects the site or its vicinities. Previous

reports available in MGB-XI also noted the debris flow that affected Brgy. Calapagan in 2006.

Moreover, results of the 1:50,000 scale geohazard mapping, Brgys. Marayag and Calapagan were

Republic of the Philippines

Department of Environment and Natural Resources

MINES AND GEOSCIENCES BUREAU

Regional Office No. XI 669 Konsuela Bldg., Aurora Quezon Street, Davao City Tel. No. (082) 222-5601 Telefax No. (082) 221-6535 Email: mines@mgbxi.com

identified as very highly susceptible to landslide taking into account its location within the Philippine

Fault Zone.

During the undertaking, two possible temporary relocation sites were identified by the undersigned.

These are located in Po. DTM (Brgy Site) and Po. Marasigon (Ridulla property), all in Brgy. Marayag

and approximately centered in geographic coordinates 126°9'39.8" east longitude/7°9'50.377" north

latitude and 126°9'53.291" east longitude/7°9'26.713" north latitude, respectively. Po. DTM relocation

site is approximately 1km north from the barangay hall. It is situated on a relatively elevated area

bounded by gullies to the east and west. The second relocation site is located in Po. Madasigon about

400 meters NE from the barangay hall. The site is also elevated and bounded by a perennial creek to

the east. It is characterized by flat to nearly flat topography and grades to moderately steep towards

the north. However, taking into account the geologic setting of the area, earthquake-related geologic

hazards, slope failures and flooding may likely affect the area in the future.

BEVERLY MAE M. BREBANTE Supervising Science Research Specialist

“MINING SHALL BE PRO-PEOPLE AND PRO-ENVIRONMENT IN SUSTAINING WEALTH CREATION

AND IMPROVED QUALITY OF LIFE”

PHOTOS