The relative strengths of building materials in a wolf-induced windstorm are clear, thanks to the classic story of the Three Little Pigs. But how do basic buildings hold up in a more complex natural hazard such as a volcano? A new study assesses the various threats to structures during an eruption, hoping to help communities better understand their vulnerabilities.
Eruptions of explosive volcanoes, such as those that dot the Pacific Rim, feature many more hazards than lava alone. Falling ash and hot flying rock can overload or puncture roofs, while scalding flows of ash, debris or mud can pound at walls and pour through doors and windows. This is all assuming, of course, that the building under assault hasn’t already been leveled by a volcanic earthquake or a lateral blast, or buried under a landslide. Even the best-built homes face serious challenges in volcanic hazard zones.
An international team assessing volcanic risks visited the areas surrounding two active volcanoes: Kanlaon volcano in the Philippines and Fogo volcano in Cape Verde. Researchers found that most dwellings near Fogo were constructed with masonry and featured reinforced concrete roofs. Dwellings near Kanalon included some built with masonry, some built with timbers and still others built from woven palm fronds with corrugated steel as a common roofing material.
Unreinforced masonry structures with concrete roofs may be vulnerable to volcanic earthquakes, the researchers report in the Journal of Volcanology and Geothermal Research, which published their results. Timber structures may resist seismic shaking better, but are more vulnerable to ash and debris falling from the sky or flowing along the ground. Masonry structures, on the other hand, may bear ash falls just fine.