The region's volcanic quiescence was 
shattered by the sudden eruption in 
about 260 of Ilopango volcano, which 
has been studied by Virginia Steen-Mc- 
Intyre of Colorado State University. 
Under the northwest corner of Lake 
Ilopango — a lake formed as a result of 
more ancient volcanic activity — a vent 
opened up and began spewing massive 
amounts of tephra into the air. The 
eruption was rapid; it occurred in only 
two identifiable stages, with almost no 
pause in between. Because the vent was 
under water, steam explosions contrib- 
uted to the violence of the eruption, and 
the rapid cooling of magma to tephra 
by the lake waters created very small 
particles, which the wind carried long 
distances. The magnitude of the erup- 
tion can be envisioned from the three- 
foot-deep ashfall at Chalchuapa, forty- 
five miles northwest of the source. 
Eruptions can also be compared by cal- 
culating the total volume of material 
blasted into the air. Geologists estimate 
that more than a cubic mile of ash was 
released by the big May 18 eruption of 
Mount St. Helens. By comparison, Ilo- 
pango may have blasted more than ten 
cubic miles of ash into the air, making 
this eruption one of the world’s biggest 
during the past few thousand years. 
The zone nearest Ilopango was one 
of complete devastation, where plants, 
animals, and, of course, people could 
not have survived. This was where ash 
fell to a depth of 6 to 8 feet — and up to 
165 feet deep nearest the source. Al- 
though we cannot yet map its bound- 
aries accurately, we can say that this 
zone was elongated to the northwest, 
extending at least eighteen miles on 
that side of the volcano, evidence that 
the eruption plume was pushed by the 
prevailing winds of the rainy season, 
which lasts from May to November. 
The absence of pollen in the tephra also 
confirms that the eruption occurred 
during the rainy season. 
Beyond the zone of complete devas- 
tation was an area of more than a thou- 
sand square miles where most people 
would have survived, but where fields 
would have been too deeply buried by 
the white volcanic ash to be cultivable. 
If it is even a few inches deep, fresh, 
unweathered volcanic ash suffocates 
plants by interfering with transpiration, 
and adsorbed elements on the grains 
create acids when mixed with moisture. 
Windblown ash sandblasts plants and 
can topple or bury maize and other 
crops in a few days. In addition, Ilo- 
pango erupted at the worst possible 
time for the Maya farmers — during the 
rainy season when their crops were 
growing and food stores were low. 
They probably also had little stored wa- 
ter that could be used in such an emer- 
gency. Within days or weeks, thou- 
sands of people must have emigrated. 
There are some archeological indica- 
tions that the refugees moved north, to 
the Maya lowlands. Gordon Willey and 
his associates from Harvard University 
excavated the site called Barton Ramie 
in Belize and found that at the same 
time that a series of “foreign” artifacts 
showed up at the site, its population 
doubled. The intrusive artifacts stylisti- 
cally match those that had been devel- 
oped in El Salvador and were in use 
there just prior to the eruption of Ilo- 
pango. Illopango refugees also appar- 
ently settled at a number of other sites 
in the lowlands of northern Guatemala 
and Belize. For reasons we do not yet 
understand, however, there are also 
many sites in the lowlands that suffered 
a population decline about the third or 
fourth century a.d. 
The eruption forced many people to 
evacuate their agricultural lands, but in 
outlying areas, where no more than one 
or two inches of tephra were deposited, 
people could have adjusted to the 
changed conditions. The tephra would 
have caused problems for a few years, 
especially for farmers nearest the 
Above: The area dominated by the 
Maya culture encompassed both 
volcanic highlands and lowland 
terrain to the north. In about 
a.d. 260, the catastrophic eruption 
of Ilopango, a volcano located in 
what is now El Salvador, forced the 
Maya living in surrounding areas to 
abandon their farmlands for up to 
two centuries. Their major trade route, 
which led through Olmec territory 
into central Mexico, was rerouted 
to the north. These events may help to 
explain why Classic Maya 
civilization (a.D. 300-900) is 
associated with the lowland areas. 
Right: The eruption of Ilopango 
created a zone of devastation 
(gray line) and blanketed 
adjacent areas with ash. These 
lands were eventually resettled, but 
in a.d. 600 the Zapotitan Valley 
was hit by the eruption of another 
volcano, Laguna Caldera, which 
buried Ceren and other sites in 
ash (orange line). Two other local 
volcanoes erupted later in the 
valley's history, depositing ash 
in about 950 (purple line) and 
1658 (green line). 
34 
