Water Catchment and Ash

Water Catchments

Although airborne, ash will eventually land on everything in its path: roofs, porches, lawns, crops. Vehicles driving can stir up ash on roads. Residents on water catchment systems may want to disconnect their downspouts during periods when a large amount of ash is being deposited on the roof, to prevent ash from entering their water systems, which could clog plumbing and filters and damage pumps; downspouts should only be reconnected after the ash and dry-deposition aerosols have been thoroughly washed from the roof. However, Halemaʻumaʻu is currently producing a relatively small amount of ash that will likely settle into the bottom of water catchment tanks. Homeowners on water catchment may need to change filters more often, and perhaps clean the bottom of their tank periodically, as these tiny amounts of ashfall accumulate.

left: Halemaʻumaʻu ash plume, right: disconnecting a downspoutleft: Halemaʻumaʻu's plume rises above the crater on 4/24/2008. right: If your home is on a water catchment system, and a lot of sulfur-rich dry deposition and ash has been accumulating on your roof, you might want to disconnect your downspout until a good rain cleans off the residue. Reconnect to your tank when it's safe.

If an increased amount of sulfur/sulfate aerosols is landing on your roof, the water in your catchment tank will likely be more acidic than usual. You can add baking soda to your tank to help neutralize the acid rain; a box or two once or twice a month should do the trick.


The Halemaʻumaʻu plume contains not only SO2 and sulfuric acid, but intermittent ash. Ash is composed of particles of rock that are so small they can be airborne. Whereas SO2 and sulfuric acid are strong chemical irritants, ash has a mechanical, abrasive effect, further irritating the eyes and respiratory tract. If ash starts falling out of the sky in your neighborhood, the best strategy is to shelter indoors and close all the doors and windows. A household air purifier would likely help, since these are designed to reduce dust particulates from the air. If you have to be outdoors briefly during ash fall, such as to get to your car, you might wear a protective mask, such as a paper dust mask commonly found at hardware stores. But note that particulate masks do not work for vapors—they won’t keep SO2 out. Also, these paper dust masks are intended for larger particle sizes (dust from sanding); the particulates in vog are smaller, and a dust mask won’t be effective on these smaller particles.

In other countries, volcanoes sometimes produce enormous amounts of ash, with disastrous effects on human health. The ash can clog gutters and even collapse roofs, particularly when the ash absorbs rainwater and becomes heavy. Fortunately, so far Halemaʻumaʻu is not producing large quantities of ash. Old-timers on Hawaiʻi island have a practical approach, and recall sweeping roofs and gutters to clear accumulations of ash and Pele’s hair during past events of Puʻu Ōʻō and Kīlauea summit. Homeowners on water catchment systems have additional concerns about SO2 and ashfall.

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