ICE TSUNAMI IN THE ALPS - Tambora: The Eruption that Changed the World - page 93

By the time the dam ultimately burst, Venetz's tunnel had reduced its volume by a full third,
sparing the valley a worse calamity.
Because Venetz could not quite save the day. The water coursing through the tunnel, com-
bined with that continually cascading from the Giétro glacier above and through myriad oth-
er cracks in the ice, dramatically reduced the thickness of the wall until finally, at 4:30 in
the afternoon of June 16, the frozen edifice suddenly collapsed with an enormous, deafening
crash. Fifteen million cubic meters of heaving water, ice, and mud thundered down into the
Val de Bagnes. Venetz and his workers scrambled to higher ground and watched in horror
as the pent-up River Dranse, now a hundred-foot-high tsunami, rushed through the gorge,
dragging boulders and great blocks of glacial ice with it before launching itself with a roar
into the valley. The old stone bridge at Lake Mauvoisin was smashed in an instant. Dozens
of hillside chalets fell victim to the great onrushing tide, while in the valley farmhouses and
barns bobbed on the torrent like giant toys. The flood ripped entire forests from their roots,
as glossy orchards and fields of wheat and grain were submerged, including the family farm-
lands of Jean-Pierre Perraudin.
By the time it reached the plain, the flood had assumed a truly sinister character: an ooz-
ing lake of black mud filled with rocks and tree trunks churned toward the River Rhône at
Martigny, accompanied by a thick, black fog. Vital infrastructure and industries of the val-
ley—roads, bridges, sawmills, flour mills, and an ironworks—sank beneath the miasma. In
the words of one eyewitness the entire valley, “but a moment before so beautiful and so pop-
ulous, was converted in a moment into a dreary desert.” 19 In Martigny, this wall of mud, ice,
and dangerous debris flooded the streets and houses, reaching up to the second story.
The icy deluge took half an hour to pass. It spilled across the River Rhône, and only
exhausted its destructive rage on reaching Lake Geneva around midnight, into whose vast
depths it was finally absorbed. It left behind a sixty-kilometer plain of utter devastation, filled
with thick mud, the detritus of houses and furniture, piled-up ice, rocks, and vegetation, and,
inevitably, the corpses of men, women, and thousands of animals. Lulled by the apparent suc-
cess of Venetz's tunnel, the early alarm system in the valley had failed, giving the remaining
residents minutes rather than hours to escape. Most villagers had already relocated into the
hills, however, and so the human tragedy was not on the scale it might have been. Venetz's
brilliant, brave engineering on the dam had certainly saved Martigny, the largest town in the
valley, from total destruction.
Nevertheless, the impacts of the Giétro debacle were devastating enough. A full decade
after the event, an English travel writer named William Brockedon was struck by the whole-
sale “desolation and dulness” he encountered in the Val de Bagnes, especially as compared
to the picturesque beauty of the neighboring valleys. Ascending the paths that crisscrossed
the now becalmed River Dranse, he came across the ruins of a stone house, which stood like
“an object of malediction,” and symbolized “the desolate and ruined state of the valley.” He
itemized the geological changes wrought by the 1818 debacle:
Vast blocks of stone, which were driven and deposited there by the force of that inundation,
strew the valley, and sand and pebbles present an arid surface where rich pasturages were
seen before the catastrophe. The quantity of the water suddenly discharged … and the velo-
city of its descent, is a measure of force which it is difficult to conceive. 20