Cotopaxi:
Ecuador’s Unavoidable Catastrophe?
Three hours after dark on November the
13, 1985, two explosions rocked a handful of sleepy villages tucked into the
folds of Nevado del Ruiz, a volcano located 150 kilometres west of Bogota,
Colombia. In the seconds that followed, Ruiz blasted thousands of tons of ash
and debris more than six kilometres into the sky and spewed fiery pyroclastic
flows onto the glacier crowning its summit; the steam and lava melted hundreds
of tons of snow and ice almost instantly, sending water raging downward through
the streams radiating out from the volcano’s rocky skirt.
By the time the flood reached the town of Chinchina,
30 kilometres west of the volcano, it had accumulated mud and rocks and
converted into a cataclysmic debris flow, called a lahar, that poured over the
town killing 2.000 of its citizens and carrying away whole neighbourhoods. One
hour later, another lahar devastated the nearby city of Armeno. When the lahar
emerged from a deep gorge above the city it was a 40-meter-high wave racing at
27.000 cubic meters per second. Within minutes it swamped almost all of Armero
and consumed 23.000 slumbering people.
If authorities do not take preventative measures soon,
the death and destruction caused by Ruiz will pale in comparison to what
happens when Ecuador’s Cotopaxi erupts again.
The avenue of the Volcanoes.
Ecuador boasts one of the highest
concentrations of volcanoes of any nation on earth; some 250 volcanoes are
crowded into an area no larger than the state Colorado. Many of Ecuador’s
largest volcanoes jut forth from the high-altitude grassland along the
country’s 400 kilometre long Central valley, aptly christened “The Avenue of
the Volcanoes” by the German explorer Alexander Von Humboldt. Cotopaxi, the
grandest volcano of them all, resides just 60 kilometres south of Quito,
Ecuador’s capital. At 5.897 meters, Cotopaxi’s majestic cone holds the
distinction of being the highest active volcano on the planet.
Active volcanoes are spatially associated with major
tectonic plate boundaries and draw their energy from the movements and
collisions of the plates. Ecuador is peppered with 26 active volcanoes because
it sits atop the convergent plate boundary where the denser Pacific oceanic
plate slips slowly beneath the South American continental plate. Rock on the
upper surface of the subducted plate is dragged downward into the earth’s crust
until it reaches the upper mantle where it is liguefied. The molten rock then
periodically rises along vertical shafts in the earth’s crust and is ejected
through volcanic craters resulting in violent ash and spectacular lava
eruptions.
Ash eruptions occur when molten debris, ash, cinders,
and rocks (referred to as “bombs”) highly charged with steam and other gases
are shot out of a volcanic crater. On November 3, 2002, the unexpected eruption
of the volcano Reventador, located 90 kilometres east of Quito, brought central
Ecuador to its knees. Within a few hours, a 25.000-square kilometre cloud
blanketed the entire region, including Quito, with several centimetres of ash.
In a lava eruption, fiery lava spills over the rim of
a volcano’s crater or flows through a crack in the side of the volcanic cone
putting on a dazzling show for onlookers. Lava eruptions may go on for days,
weeks, or even years. This kind of eruption is particularly common among shield
volcanoes, such as those that make up the Hawaiian and Galapagos Islands. The
volcano Tunguragua located on the outskirts of Banos, a small city on the
eastern slope of the Ecuadorian Andes, also regularly produces lava eruptions.
While ash and lava eruptions frequently damage property they are not terribly
dangerous – only a few people have died as a result of the recent eruption of
Revantador and the ongoing eruptions of Tunguragua – and they have never caused
a disaster comparable to those that have been provoked by lahars.
A lahar is not a type of eruption but rather a flow of
volcanic debris that forms when large quantities of water mix with the ash,
rock, and earth found on the slopes of a volcano. As water rushes down the
sides of a volcano it picks up increasingly larger debris until it thickens
into a flow with the consistency of wet concrete. Once formed, a lahar can
reach speeds of up to 60 kilometres per hour, swell to heights of 80 meters in
confined spaces, such as riverbeds and canyons, and travel as far as 300
kilometres. Lahars sweep up everything in their path and have been known to
carry huge boulders as large as 50 meters in circumference as far as 20
kilometres.
Lahars can occur when torrential rains wash down ask
from previous volcanic eruptions; when pyroclastic flows mix with a river; or
when an eruption ejects a crater lake. A lahar can also be triggered by a rise
in temperature on the surface of the volcano that melts the glaciers that have
accumulated on its flanks. This is what happened at Ruiz and what geologists
fear from Cotopaxi.
Cotopaxi: Ecuador’s Ruiz?
Cotopaxi and Ruiz share many
characteristics; glaciers of comparable size cap both volcanoes, they are both
active and have caused lahars in the past, and, most importantly, they are both
located in densely populated areas.
Over the past 500 years, Cotopaxi has produced 30
significant eruptions. At least twenty of these have triggered lahars. During
an 1877 eruption of Cotopaxi, a lahar killed 1.000 people when it engulfed the
city of Latacunga. Another lahar caused by same eruption reached the Pacific
ocean near the city of Esmeraldas, more than 250 kilometres northeast of the
volcano.
The toll from Cotopaxi’s lahars has not reached the
scale of Nevado del Ruiz only because of the demographic differences in the
affected areas at the time of the volcanoes’ respective eruptions. The 1877
eruption killed 1.000 people in an area occupied by a few sparcely populated haciendas
and small towns. Since 1877, the population in the footprint of the Cotopaxi’s
past lahars has soared from approximately 30.000 to more than 500.000.
During a significant eruption, everyone living within
a hundred kilometres of Cotopaxi would face choking ash and a full fifth of the
half million residents living in the valleys west of the volcano would be at
risk of being swept up in lahars. Most of the 100.000 people in danger from
lahars have built their homes and business on top of laharic deposites by past
eruptions and in the floodplains of local rivers, the principal paths of
lahars. They may escape but their homes and property will be demolished.
Not if but when?
Immediately after the catastrophe at
Ruiz, Geologists began studying Cotopaxi more intensely than ever. Over the
past 25 years they have learned much. Scientists have made important
discoveries by examining the geologic history of the volcano and surrounding
area. This research has allowed them to map the paths of the past lahars and has
given them some clues to the frequency with which Cotopaxi erupts. The body of
knowledge is particularly deep dating back 500 years, thanks to detailed
accounts of Cotopaxi’s eruptions kept by the Catholic Church. Since the arrival
of the Spanish, Cotopaxi has manifested six periods of significant activity.
Three brief periods: 1532 – 1534, 1698 and 1803; and three longer periods: 1742
– 1768, 1845 – 1886, and 1903 – 1914. After
decades of silence, Cotopaxi has awoken. Since November 2001, scientists
have documented dramatic increases in seismic activity in the vicinity of the
volcano and fumarolic activity from Cotopaxi’s crater. They have also recorded
several small explosions and a growing bulge on the volcanic cone.
According to Steven Brantly, from the United States’
Geological Survey´s Volcano Disaster Assistance program, “Based on about 25
years of monitoring, Cotopaxi recently entered into a phase of unrest
heretofore unseen.”
Dr. Theofilos Toulkeridis, a professor of geological
sciences at Quito’s University of San Francisco, concurred with Mr. Brantkey’s
appraisal and pointed out that Cotopaxi´s last four intervals of calm have been
much shorter than the volcano´s present 88 years of repose.
With an array of monitoring instruments
recently provided by the USGS VDAP, Ecuadorian and foreign scientist monitor
Cotopaxi 24-hours a day. They will know of any significant change in activity
within minutes. Unfortunately, this
will be too late.
According to Dr. Toulkeridis, “New
numerical simulation studies indicate that major villages will be hit in less
than 30 minutes from its [lahar] start near Cotopaxi´s crater but that less
than 15 minutes would be available for the warning of the population from its
real detection due to the undetectable start of the subglacial part of the
flow.”
If a recent evacuation exercise
undertaken in June 2002 is any indication what should be expected in an actual
eruption, tens of thousands will perish. Just 7.000 people participated in the
exercise and, even under the optimal conditions of the drill, the authorities
needed 1-2 hours to direct the evacuees to the designated safe zones.
Dr. Toulkeridis confirms that because of the very brief time between the
formation of a lahar and when it would strike the population “evacuation plans
will not help to prevent this very potential catastrophic event.”
Evacuation may be hopeless but the
situation is not. Dr. Toulkeridis, who has long been urging the civil
authorities to take preventative measures, asserts that “protective walls in
form of ‘giant sieves’ will be able to
partially stop and chanalize lahars before any
life or property is in danger.”
A few countries, such as Japan, that face
constant volcanic threats have developed effective means of mitigating the
impact of lahars. Structures can be built to divert lahars away from populated
areas and to filter out boulders and debris before they reach population
centres. The construction of these devices has never been seriously considered
in Ecuador because of the cost. Needless to say, the consequences of the lahars
that could be triggered by Cotopaxi´s impending eruption will greatly surpass
the costs of even the most comprehensive mitigation measures.
Without the necessary bulwarks and ‘giant
sieves’, the material and economic loss resulting from a future eruption of
Cotopaxi will cripple the capital region. Not only will the city of Latacunga
likely be ruined – Cotopaxi has already destroyed it five times over the past
two hundred years – but huge swaths of suburbs now occupying nearly the entire
valley north and west of the volcano will be buried. A significant lahar would
almost certainly destroy many billions of dollars worth of property and
thousands of acres of Ecuador’s most productive farmland. Moreover, tens of
thousands of people would remain displaced for years either because the volcano
continues threatening the evacuated areas or because their homes have been
destroyed.
Such dramatic effects are not far
fetched. Lahars resulting from the 1980 eruption of Mount Saint Helens, which
is located in a sparsely populated region of south western Washington state,
cost nearly one billion dollars in repairs and cleanup. The effect can be far
worse in populated areas. More than two years after the eruption of Pinatubo in
the Philippines, Philippine and USGS volcanologists reported that “thick lahar
deposits have left 50.000 people homeless, and flooding and isolation have
affected more than 1.350.000 in 39 towns and four large cities”.
Disaster or catastrophe?
The word “disaster” implies sudden,
unavoidable misfortune. “Catastrophe”, on the other hand, suggest tragedy, the
culminating end of a drama. The AD 79 eruption of Mount Vesuvius that buried
Pompeii was a disaster; nearly two millennia ago there was no way to predict it
or mitigate the death and destruction it caused. Conversely, the 1985 eruption
of Colombia´s Nevado del Ruiz must be named a catastrophe.
Armero and Chinchina were built on the
fertile alluvial plains left behind by Ruiz’s past lahars, and the volcano had
shown clear signs of activity for months before it unleashed the cataclysmic
debris flows that killed more than 25.000 Colombians. Latacunga and the
sprawling suburbs south of Quito are also built upon lahars, and, just as Ruiz did
before it erupted, Cotopaxi has demonstrated its unrest countless times over
the past months.
Which word will best describe the next
eruption of Cotopaxi?
That depends on what is done between now
and then.
From THE QUITO SUN
Cotopaxi
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