The DENR, MGB-6 team who assessed the landslide site in Tubungan, Iloilo on August 12, 2009 advised the municipal government of Tubungan, Iloilo to declare the landslide site as a ‘danger zone.’ A landslide was observed by the residents to have occurred in Brgy. Igtuble, Tubungan on August 5, 2009.
The DENR, MGB-6 team headed by a geologist Dr. Leilani O. Suerte, noted during the field survey that a huge and active landslide, at least one kilometer long, was observed in the upland sitios of Brgy. Molina and Brgy. Igtuble, Municipality of Tubungan. These areas, collectively called Bato Ritak by the locals, have very steep and rugged topography, with elevations ranging from 500-1,159 meters above sea level.
Previous geohazard assessment of the upland barangays of Tubungan conducted by the DENR, MGB-6 in 2006 and 2008 already indicated that these areas are highly prone to landslides. Landslide threat advisories and recommendations for landslide identification, monitoring and mitigation were given to the officials of the identified barangays.
During the recent assessment, Suerte reported that the landslide originated in different portions of the mountains. Some of the landslide materials came from the mountaintop and others from the mid-slope or foot slope of the mountains. The landslide debris consists of unconsolidated soil, broken rocks ranging from the size of a pebble to that of a boulder and plant materials. These are deposited at the mid-slope and foot slope of the mountains and sections have started flowing several hundred meters away from the landslide site towards Maslog Creek.
Further, she said that the main cause of the landslides in Bato Ritak and nearby areas is the very steep topography and the loose and unconsolidated soil and broken rocks underlying the area. A natural spring is also present in Bato Ritak. The recent occurrence of heavy rains added to the abundant spring water, further weakened these materials and hastened their downward movement.
She also noted that even without rain, the inherent topography together with the types of soil and rocks in the area are sufficient to trigger mass movement in Bato Ritak and other localities with similar characteristics. Thus, occurrences of landslides can be expected in such areas.
In Bato Ritak, the rapid movement and huge volume of falling materials created rumbling sounds. Dust from the falling debris appears smoke-like when viewed from a distance. Thus, residents reportedly hear thunderous sounds and saw smoke coming from the landslide site, Suerte further explained.
The DENR, MGB-6 team informed the residents that the landslide area is large and there is a huge amount of landslide debris. During continuous and heavy rain fall in the landslide site, barangays Igtuble and Molina in the said municipality may also experience other hazards such as flashfloods and mud flow as water and landslide materials will move towards Maslog Creek and maybe Tigbalabao Creek.
There is also a need to identify an alternate entry and exit road leading to barangays Igtuble and Monia. The existing road was destroyed by the mud/debris flow, isolating the residents from the rest of Tubungan.
DENR, MGB-6 also recommended that visitors must not be allowed in the area except for those posted as guards or assigned to monitor the progress of the landslide.
The team further advised that the water level and turbidity in springs, creeks and rivers must be constantly monitored. Communities, especially those along the Maslog Creek and Jar-ao River must be warned of the progress of the landslide and they must prepare for evacuation at all times. The residents must also inform immediately the concerned authorities if the condition worsens.
The municipal government of Tubungan, Office of the Civil Defense and the Jaro Social Action Center requested for the DENR, MGB-6 to assess the landslide area.
Regional Director Leo Van V. Juguan of the DENR, MGB-6 said that the information generated from the geohazard assessments will help the local government units and communities living in areas prone to geologic hazards to come up with a disaster preparedness plan to avoid damages to lives.