Bulletin of the Geological Society of Malaysia, Volume 69, May 2020, pp. 111 – 124
Tajul Anuar Jamaluddin*, Norasiah Sulaiman, Nor Shahidah Mohd Nazer
Program Geologi, Jabatan Sains Bumi dan Alam Sekitar,
Fakulti Sains dan Teknologi, Universiti Kebangsaan Malaysia, 43600 UKM-Bangi, Selangor, Malaysia
* Corresponding author email address: taj_anuar@yahoo.com
Abstrak: Tanah runtuh lama adalah tanah runtuh yang berlaku, mungkin puluhan atau ratusan tahun yang lalu dan boleh diaktifkan semula oleh penyebabnya yang asal atau penyebab lain. Kewujudannya geobahaya ini sering terlepas pandang disebalik kerencaman topografi dan litupan tumbuhan yang tebal di kawasan tanah tinggi tropika. Kemahiran asas geomorfologi dan pengalaman diperlukan untuk mengecam dan memetakan tanah runtuh jenis ini kerana fitur-fitur geomorfologi yang berasosiasi dengannya telah diubahsuai akibat proses luluh hawa, hakisan dan pemendapan yang pesat di rantau tropika. Pembangunan infrastruktur di kawasan berbukit dan tanah tinggi di Malaysia akhir-akhir ini secara tidak langsung mendedahkan pelbagai masalah geoteknik dan risiko geobencana susulan pengaktifan semula tanah runtuh lama. Tanah runtuh lazimnya menghasilkan tanda-tanda yang boleh dilihat dan boleh dikenalpasti melalui cerapan morfologi dan corak topografi cerun bukit secara teliti. Penggunaan kaedah penderiaan jauh dan fotogrametri dron sangat membantu dalam proses pencerapan morfologi tanah runtuh lama. Sesebuah tanah runtuh, sama ada yang baru atau lama mempunyai himpunan fitur-fitur geomorfik tersendiri, bergantung kepada jenis, saiz dan usia kegagalan dan skala cerapan. Fitur-fitur
seperti kerawang di bahagian kepala, tubir utama, tubir sisi, cerun cekung dibahagian tengah, dan disusuli dengan topografi cembung dan beralun di bahagian kaki cerun adalah petunjuk utama untuk mengenalpasti kewujudan geobahaya tanah runtuh. Tanda-tanda lain seperti kehadiran longgokan kolovium di kaki cerun atau di lantai lembah, anak-anak sungai bercabang bentuk-Y di bahagian hulu cerun, kewujudan teres-teres bertingkat, perbezaan kepadatan tumbuh-tumbuhan dengan cerun sekitarnya, juga boleh dijadikan petunjuk untuk mengenalpasti tanah runtuh lama dan menganggarkan usia relatifnya sama ada muda, dewasa atau tua. Penilaian geomorfologi daripada kawasan Cameron Highlands dan Kundasang dibentangkan untuk dijadikan panduan bagi mengesan dan mengenalpasti kehadiran geobahaya tanah runtuh lama serta dipetakan di dalam peta inventori tanah runtuh sebagai sebahagian maklumat asas geobahaya.
Katakunci: Fitur geomorfologi, geobahaya, tanah runtuh lama
Abstract: Past landslides are old landslides, probably decades or hundreds of years ago that could be reactivated by their original causes or other causes. Their occurrences are often overshadowed by topographic complexity and dense vegetation cover in the hilly tropical terrain. Basic skills in geomorphology and experience is needed to recognize and identify this type of landslide because the associated geomorphic features tend to be mollified by intense tropical weathering, erosion and rapid sedimentation of the tropical region. Infrastructural developments encroached into the hilly terrains of Malaysia recently has indirectly expose various geotechnical problems and geodisaster risks due to reactivation of the past landslides. Landslides often produced visible signs and can be identified through detailed observation on the morphology and hill slope topography. The aid from new and advanced remote sensing technology and drone photogrammetry making geomorphological observation of past landslide in remote natural terrains easier and more convincing. A landslide, whether new or past, is often characterized by an assemblage of distinct geomorphic features depending on its type, size, age and scale of observation. Features like arcuate crown and main head scarp, side scarps, concave upper slope, convex lower slope and followed by undulating hummocky topography near toe are amongst the main signature to identify the existence of landslides geohazard. Other signs inclusive of colluvial deposit at the foot of the slope or in the downstream floor valey, Y-shaped bifurcating streamlets in the upstream, the existence of stepped terraces, different vegetation cover to the
slope counterparts, can also be used to identify and to estimate the relative age of past landslides, either young, mature or old. Geomorphological assessment from Cameron Highlands and Kundasang areas are presented herein as a guide to recognize and identify the existence of past geohazard and mapped into landslide inventory as part of fundamental information for geohazard.
Keywords: Geomorphic features, geohazards, past landslides
DOI: https://doi.org/10.7186/bgsm69202010
