Origin and early evolution of lahar channel at Mabinit, Mayon Volcano, Philippines

Research Article| March 01, 1989 Origin and early evolution of lahar channel at Mabinit, Mayon Volcano, Philippines KELVIN S. RODOLFO KELVIN S. RODOLFO 1Department of Geological Sciences, University of Illinois at Chicago, Box 4348, Chicago, Illinois 60680 Search for other works by this author on: GSW Google Scholar Author and Article Information KELVIN S. RODOLFO 1Department of Geological Sciences, University of Illinois at Chicago, Box 4348, Chicago, Illinois 60680 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1989) 101 (3): 414–426. https://doi.org/10.1130/0016-7606(1989)101<0414:OAEEOL>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation KELVIN S. RODOLFO; Origin and early evolution of lahar channel at Mabinit, Mayon Volcano, Philippines. GSA Bulletin 1989;; 101 (3): 414–426. doi: https://doi.org/10.1130/0016-7606(1989)101<0414:OAEEOL>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Mabinit Channel, 5 km long, 15 to 70 m wide, and 2 to 22 m deep, was formed by lahars on the southeastern slope of Mayon Volcano during its 1984 eruption. In 1985, the channel was drastically modified by a lahar triggered by a typhoon. Sediment-budget calculations from surveys conducted in 1985 and 1986 corroborate inferences from other volcanoes that lahars can grow significantly in volume by eroding their channels.The 1984 eruption produced a deep summit ravine and, at its base, a fan of avalanche and pyroclastic-flow deposits 2 km2 in area and 40 x 106 m3 in volume. Lahars initiated in the ravine by heavy rains from eruption updrafts carved out 5-km-long Mabinit Channel along the west margin of the pyroclastic-avalanche field, a position that could not have been predicted from pre-eruption topography. By eroding the channel, the lahars generated more than half of their own solid contents. Below 240 m, where the volcano slope decreases from 5° to 3°, the first eruption debris flows were unconfined and spread out over a 512,000-m2 area, depositing a layer locally more than 4 m thick with a volume of 1.25 x 106 m3. The thin margins of these unconfined flows were non-erosional; however, as they stopped, their thick central portions continued flowing, extending the new channel downslope through the depositional field. Subsequent eruption lahars modified the channel and overflowed at its bends.A moderately intense typhoon in October 1985 triggered a single 9-hr lahar event that widened the channel by an average of 25 m and caused as much as 66 m of lateral bank erosion. Debris flows overtopping the channel at four sites coalesced to cover a 2-km-long, 200,000-m2 area with bouldery sediment. In wider channel stretches, debris-flow margins left prominent paired levees, while their central portions continued moving down-channel as rigid plugs. The lahar plugged the lower 0.5-km stretch of the channel and replaced it by eroding a new channel of comparable size. This demonstrated how easily lahars can change the courses of channels on the upwardly convex debris apron of a stratovolcano, with serious consequences for farmland and communities. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.