The Voice of this Stone

11 June 2019


The community of Orting, Washington in 1994 with Mount Rainier (America’s most dangerous volcano) in the distance. The floor of the Puyallup and Carbon River valleys consist of about 1 to 5 m of Electron Mudflow deposits.


Some stones, real as well as metaphorical, should be required reading (and listening) for emergency managers...

The most famous is the Granatello Epigraph, a stone billboard erected by the Spanish Viceroy in a Naples suburb in 1632, shortly after a major eruption of Mount Vesuvius. It warns, “Descendants, descendants, listen to the voice of this stone. When the volcano shakes, roars, rumbles, leave your home and possessions, and run away without delay…”

I was inspired to write The Voice of This Stone as I walked the deserted streets of Beichuan, China, once home to about 200,000 souls, and now empty. Beichuan was preserved as a “disaster museum,” a lesson of where not to build a city: in this case, in a deeply incised canyon at the edge of the Tibetan Plateau. I knew that I was walking on sacred ground. Some 15,000 to 20,000 people lay unrecovered in the debris of the destroyed city.

In those sobering moments, I decided that sharing what I’ve learned from my career as a geologist would save lives. These lessons had come from responding to nearly all the post-1980 volcanic disasters around the Pacific Rim of Fire, comparing them with many eruptions of Vesuvius and Campi Flegrei. My fifty-year career as a geologist with the United States Geological Survey (USGS) is unusual in that I worked as a field geologist. It is in the field that we discover the deposits of previous eruptions and obtain a record of a volcano’s past that may extend for millennia. We know that a volcano’s past is key to its future.

The messages they offer are many. The most unambiguous are “tsunami stones.” These are stella placed by survivors to mark the peak runups of tsunamis in Japan to show future generations where it will not be safe to build. Unfortunately, TEPCO, the Tokyo Electric Power Company, ignored this evidence, which revealed tsunami heights from at least 869 CE. The utility company chose to construct nuclear reactors at such a low level that three reactors suffered meltdowns after the Great East Japan Earthquake of 2011.
Other readable “stones” are found in the deposits of volcanic ash, debris flows (lahars), debris avalanches, and volcanic landslides that are the products of past eruptions. They are forensic evidence of how a volcano has behaved in the past, and how it is likely to behave in the future. Armed with knowledge, we can plan the most effective mitigation measures for the future.

The most egregious example of failing to read the stones of the past is what Barry Voight, emeritus professor of geology at Pennylvania State, describes as the “day of reckoning.” That day was November 13, 1985, when 21,000 residents of Armero, Colombia (70 percent of the population), were killed by lahars at the base of the huge stratovolcano called Nevado del Ruiz. In this case, warnings from the “stones” were painfully obvious—twice before in recorded history Armero had been destroyed by lahars, and their deposits were preserved as layers of bouldery mud in 1595 and 1845. These deposits and their origin were not recognized before, and in each case Armero was rebuilt. Finally, the people understood the danger of rebuilding in the same location, and Armero was not reconstructed.

As lahars raced down the flanks of Nevado del Ruiz, there was no warning. There was, however, one last chance. Boulder-sized “stones” in the surging mass of mud were colliding, creating ground tremor so strong that as far as a kilometer away, people were knocked to their knees. Jack Lockwood, my USGS colleague, had interviewed survivors and reported that as many as half of those perishing in Armero could have saved themselves had they immediately recognized the origin of the ground tremor and gone to high ground before the lahar arrived. Now we know ground tremor as a warning voice from the stone.


Volcanic cone

The most dangerous volcano in the United States is Mount Rainier. That volcano has a history of huge collapses that transform into lahars that are sufficiently mobile to flow all the way to Puget Sound. The lahars flow long-distances in the valleys draining the volcano that I like to call lahar pathways. Large lahars have a recurrence interval of about 1,000 years during later post-glacial time, the last 6,000 years. Homes and businesses are rapidly springing up in the pathways despite land-use restrictions. Consequently, the numbers at risk steadily increase while the volcano’s hydrothermal plumbing system continues to weaken the edifice. Risk is also increased by the fact that the collapses may not be associated with precursory activity that would make pre-event evacuation possible. Given this situation, warning can only come from an “event-warning system” (as “It is happening now!”). We have established an event-warning system at Mount Rainier, consisting of Acoustic-Flow Monitors (AFMs), the small seismometers used in oil exploration. AFMs can detect the ground tremor of an approaching lahar, launching a siren warning to downstream populated areas. More than twenty sirens have been installed; an additional twenty are planned.

The bane of emergency managers is what we call the “false-alarm problem.” Warnings of a volcano eruption may be correct, or they may be incorrect. Volcanic activity tends to wax and wane, and the cases where precursory activity ramps up continuously to an eruption are not common. Authorities may be reluctant to warn of an eruption out of fear that their alarm may be a false alarm. For example, at Mount Rainier, evacuating the areas at risk of a large lahar would disable an economy of regional scale. Barry Voight sums up the issue by asking, “What do you cry when there MAY be a wolf?” At Mount Rainier, the lahar-warning system with the AFM network will only warn when a wolf is actually on the way.

The false-alarm problem is manifested most dramatically where an eruption occurs with no warning. If this happens in Japan, those who fail to provide a warning are advised to commit hari-kari (ritual disembowelment). There are three ways things can go wrong: 1. An eruption occurs with no warning. 2. Fear of a false alarm prevents a warning. 3. A warning is made but no eruption occurs. There is only one way things can go right: a warning is made and an eruption occurs.

The AFM network provides certainty that a large lahar has been spawned by collapse of the volcanic edifice. At the base of Mount Rainier, for a lahar warning to be triggered, three high-level AFMs must register the ground tremor from a flowing lahar in sequence, upstream to downstream. Two “deadmen” instruments at a lower level must go dark in sequence. The signals are radioed to a 911 call center where they are evaluated by a human before the sirens are sounded. The lahar pathways will then be evacuated, probably with the chaos well portrayed in the movie Dante’s Peak. Authorities could not make the leap to a lahar warning without evaluation by a human. Unfortunately, the weak link in many warning systems is the human, and cases of warnings claimed to have been sent, but not received, is an old story. The lahar-warning system at Mount Rainier will give those living in lahar pathways, like those in the city of Orting, about thirty to forty-five minutes to evacuate to high ground.

The cities of Pompeii and Herculaneum, destroyed in 79 CE by a huge eruption of Mount Vesuvius, are disaster museums, although not publicized as such like Beichuan, China. The city of Naples, Italy, sits between Vesuvius to the east, and the supervolcano of Campi Flegrei to the west. Of the two famous volcanoes, Campi Flegrei ranks higher in terms of risk. It erupted 150 cubic miles of the Campanian Ignimbrite 40,000 years ago, hypothesized to have caused the extinction of the Neanderthals. It also produced the Campanian Yellow Tuff 12,000 years ago, a prominent building stone in Naples. The most recent eruption occurred in 1538. Vesuvius has not been active since 1944. Campi Flegrei, however, threatened to erupt in 1983 when the center of the caldera began rising vertically in response to what is called bradyseismism. An earthquake accompanying the uplift in 1983 triggered evacuation of 40,000 people from the city of Pozzuoli when it looked like an eruption could occur.


Snow-clad volcano

In the center of Pozzuoli, three vertical columns record bradyseismic activity and serve not as a disaster museum, but as a reminder of the continuing presence of an active body of magma in a supervolcno several kilometers in depth. The lower portions of the columns, known as the Temple of Serapis or the Pillars of Wisdom, are scarred by boring marine mollusks, showing that they were submerged below sea level following their construction by the Romans ca. 100 BCE, and have been subsequently raised above sea level.
As development indefatigably encroaches on Vesuvius and in spite of the threatened eruption of 1983, also in Campi Flegrei, is the stage being set for another disaster? Is Vesuvius, with its complete inactivity since 1944, setting a trap? It is difficult to conclude that that present trends of people living on the flanks and in the calderas of active volcanoes are not going to end badly. “Live in danger. Build your cities on the slopes of Vesuvius,” said German philosopher Friedrick Nietzsche.
In my book, I describe actions that can reduce (hopefully greatly so) death and destruction from Vesuvius and Campi Flegrei. There is no substitute for educating the populace about the risks, and to do this, I propose a series of fact sheets that describe the hazards. There have been many warnings, manifestos, and documents that have attempted to do this, but so far have failed.

Through The Voice of This Stone, my hope is to draw attention to the histories of volcanoes around the world in these unique case studies. The rock record and recorded human history offer us warning, and thousands of lives can be saved if we heed them. Studying the past, we can know what the volcano recommends for mitigation designed specifically for the future eruptions and collapses. The stones are speaking.


Voice of this Stone


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