IN THE EARLY morning of February 21st, 2005, residents living in the shadow of the massive Leuwigajah dumpsite near Bandung, Indonesia awoke to the sound of muffled blasts -- one, two, three of them -- in rapid succession. The blasts heralded a new sound, akin to an oncoming freight train. On it came, deafening, unceasing. For many of those people, it was the last sound they would ever hear.

In a torrent of flame, refuse, and melted plastic, 143 people and 71 houses were buried in a matter of seconds, crushed under an avalanche of trash that, when settled, extended 1000 meters and rose over thirty feet high. In a painful piece of irony, almost all those who died were scavengers who made a living by scouring the gigantic dumpsite for anything of value. They lost their lives to that which had previously sustained them.

The waste avalanche at Leuwigajah was not the first tragedy of its kind, nor was it the deadliest. That macabre distinction goes to the Payatas disaster, which occurred five years prior in the Philippines and claimed the lives of 218. The Leuwigajah incident was the largest, however -- over 2.7 million cubic meters of waste material was jettisoned during the slide. More recently, it became the best studied, with a new, probing report just released in the journal Geoenvironmental Disasters.

IN THE DAYS, weeks, and months preceding the avalanche, the Leuwigajah dumpsite was receiving nearly 4,500 tons of solid waste per day. Though the site started off well managed when it was set up in 1987, it eventually fell into bureaucratic disarray. By 2000, three different authorities were depositing trash in a haphazard fashion. Each shirked responsibility.

As the mountain grew, smoke began emanating from the hulk and fires sprung up at odd times. Decomposing waste produces methane, a flammable hydrocarbon gas which can ignite with just a spark. Franck Lavigne, a physical geographer at the University of Paris and lead author of the report, also suggests that oxygen may have started accumulating deep within the mountain of trash, creating a contained combustion zone. This centralized uptick of oxygen likely fueled the rise of aerobic bacteria, which then produced heat, along with toxic gases like carbon monoxide.

According to Lavigne, the build-up of gasses likely transformed the dumpsite into a ticking time bomb that could be set off with the slightest prod. That prod eventually came, surprisingly, in the form of rain.

Here's what Lavigne thinks happened on that fateful February morning:

(1) Heavy rainfall on the dumpsite led to increased water percolation through the waste material.

(2) The percolating water reached the top of the combustion zone deep inside the waste mass.

(3) The vaporization of the water produced an increase of gas pressure at the base of the dump that probably lifted up a part of it, resulting in a sound-like explosion during the liberation of the accumulated pressured gas.

(4) The vaporization and the lift up processes combined their effects to bring air to the combustion zone. The second and probably the third explosion then occurred.

(5) As the destabilized mass began to slide, the fire propagated to the whole moving mass, helped by the significant amount of methane trapped in the waste material (numerous swirling flames were reported by eyewitnesses and were probably due to the gas trapped in the plastic bags).

(6) The combustion of each plastic bag within the moving mass produced gas that allow an expansion of the whole mass to occur. Once started, this mechanism, as well as water vaporization, triggered a self maintaining expansion during the transport. This self maintaining expansion... determined the unusually high mobility of the moving mass and can also explain why the whole material was deeply burned.

Lavigne also thinks it's possible that the added weight of the water alone could have triggered the avalanche, which subsequently released the trapped methane and carbon monoxide gasses, creating the flaming inferno that accompanied the torrent of trash.

AFTER THE 2005 avalanche, the Leuwigajah dumpsite was abandoned and has since been reclaimed by natural vegetation. Greenery now conceals the scarred landscape. From far overhead, one can hardly surmise that the area once hosted such a horrible tragedy.

Sadly, local officials seem to have forgotten, too.

"Most of the other open dump sites in Indonesia are still uncontrolled, and therefore constitute a significant hazard for many communities," Lavigne says.

In fact, four more slides have occurred at other dumpsites in Indonesia since the Leuwigajah waste avalanche, resulting in 33 deaths.

Lavigne urgently recommends that all uncontrolled dumpsites be transformed to controlled landfills. People don't always consider how much or what they throw away, but it's vital that we manage that waste responsibly.

Source: Lavigne et al. "The 21 February 2005, catastrophic waste avalanche at Leuwigajah dumpsite, Bandung, Indonesia." Geoenvironmental Disasters 2014 1:10.

(Images: F. Lavigne, Google Earth)