09 April 2017

The Volcano in Lipa City You Probably Never Knew Existed

Anilao Hill.  Image by Cesar C. Cambay directly loaded from panoramio.com.

Just so I do not get accused of panic-mongering at a time when earthquake swarm has become a fashionable term in Batangas, Phivolcs lists this volcano in Lipa City as inactive.1 It is a mound of earth called Anilao Hill south of the poblacion in the Anilao area between Antipolo del Norte and Antipolo del Sur. Phivolcs gives its coordinates at 13°54' 121°11', which is erroneous because it falls on a piece of flat land.

The Phivolcs coordinates for Anilao Hill are slightly off.  Image credit:  Google Earth.

Geoview.info gives more accurate coordinates up to the seconds at 13°54'33.48" 121°10'41.16"2. Plotted on Google Earth, this yields a mound of earth with its curvature visible if you zoom down to an elevation of 977 feet. The image is shown below.

Geoview.info coordinates plotted on Google Earth shows an obvious mound.

The Smithsonian Institution’s National Museum of Natural History Global Volcanism Program categorizes Anilao Hill as a pyroclastic cone, the last estimated eruption of which was during the Pleistocene geologic era.3 Pyroclastic cones are also called as “scoria cones” or “cinder cones.” They “are relatively small, steep volcanic landforms built of loose pyroclastic fragments.4

As mentioned, Anilao Hill is estimated to have been last active during the Pleistocene Age. This is a geologic time span calculated to have been between 2.8 million and 11,700 years ago. This epoch is often referred to loosely as the “Ice Age.5

Anilao Hill is part of a volcanic complex referred to as the Macolod (Maculot locally) Corridor. This complex includes, among others, Mount Makiling, Mount Malepunyo, the Laguna de Bay and Taal Volcano, including the lake. Down the geologic epochs, small pyroclastic or scoria cones were formed by relatively mildly explosive or Strombolian eruptions within this complex. Other similar volcanic scoria cones that have been identified are Tombol Hill in Rosario and Sorosoro Hill in Batangas City.6

Tombol Hill in Rosario, like Anilao Hill, is also a pyroclastic or scoria cone.  Image credit:  Google Earth.

Note that Phivolcs has classified Anilao Hill as an inactive rather than a dormant volcano. The terms are often used interchangeably but they do not mean the same. A dormant volcano has been inactive for many years but has the capacity and is expected to erupt sometime in the future. In contrast, an inactive volcano such as Anilao Hill is usually not expected to erupt mostly because of the very long time that passed since it was last active.7

Notes and references:
1 “Inactive Volcanoes,” online at the Phivolcs web site.
2 “Anilao Hill,” online at Geoview.info.
3 “Anilao Hill,” online at the Smithsonian Institution’s National Museum of Natural History Global Volcanism Program web site.
4 “Pyroclastic Cones,” online at Brittanica.com.
5 “Pleistocene,” Wikipedia.
6 “The Soils of the Philippines,” by Rodelio B. Carating, Raymundo G. Galanta and Clarita D. Bacatio.
7 “What are active and inactive volcanoes?” Online at reference.com.

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