Don’t build with lahar material

As a longtime reader and admirer of the Inquirer, permit me to share these thoughts about the editorial, “Menace to public safety” (4/28/19), regarding the tragic collapse of Chuzon Supermarket in Porac, Pampanga, on April 22.

It is true that bad construction materials must be blamed for the collapse, because the building should have withstood an earthquake of magnitude 6.1.  You speculate that substandard steel “rebars” used to reinforce the concrete  were to blame.  That may or may not be true in part, but, as a longtime geologist and student of Pinatubo and its lahar, I must say: It is more certain to blame the sand and gravel from lahar deposits that were used to make the concrete.  Lahar material is abundant in Porac; in fact, the town was almost completely buried by lahar after the 1991 Pinatubo eruption.

Lahar sand and gravel are the worst material to use for any concrete building component that has to bear weight.  That is because that stuff is mostly sand- or gravel-sized pieces of pumice, which was lava full of bubbles before it cooled and hardened into rock  (parang ampao, baga). The material makes good lightweight hollow blocks, but can easily be crushed if it has to bear weight and undergo the abnormal stresses during an earthquake.

For many years after the 1991 quake, I was horrified to watch countless trucks of lahar material bound for Metro Manila to use for housing and infrastructure concrete.  If and when the major earthquake that Phivolcs warns may happen at any time, Pinatubo, coupled with greed and carelessness, will claim many more victims as these structures collapse.

For God’s sake, if you live or work in a high-rise  built since the early 1990s, you owe it to your loved ones and yourself to find out if the building’s concrete  was made with lahar material.  If it was, either move out, or at least be aware of the risk.

If any good can arise from the tragic loss of life in Porac, it will be the life-saving lesson it has taught us: Not to build load-bearing concrete with lahar material.

KELVIN S. RODOLFO, PhD,

Professor Emeritus of Earth and Environmental Sciences, University of Illinois at Chicago

Senior Research Fellow,

Manila Observatory,

krodolfo@uic.edu