Geology and Civilization Part 7: Living on the Edge

Part 1, Part 2, Part 3, Part 4, Part 5, Part 6

On March 22, 2014, at 10:37 AM, a massive mudslide occurred 4 miles east of Oso, Washington. It engulfed a rural suburb of the town, killing 43 people and destroying even more homes. It was the deadliest single landslide in American history (outside ones caused by volcanoes, earthquakes, and dam collapses), and all of those deaths could have been easily prevented.

The Oso mudslide a week after it occurred. Note that it actually flowed over the river on its path. [Image source]

Within days, county officials began claiming that it was "completely unforseen" and "came out of nowhere." One noted that "A slide of this magnitude is very difficult to predict. There was no indication, no indication at all." Except, well, there had been. There'd been a 2010 report commissioned by Snohomish County that explicitly warned that the hillside in question was one of the most dangerous in the United States, and that knowledge of its risks dated back decades- the area was even known among locals as "Slide Hill." Known mass wasting events (the larger category that includes landslides, mudslides, and more) occurred in 1937, 1951, 1952, 1967, 1988, and 2006.

The immediate causes of the disaster were fourfold- a history of past instability and structural weakness, clearcut forests along the top of the ridge, heavy rains, and the persistence of the county in allowing- and even encouraging- development in the area. While the failures of the state, county, and logging company are all depressing, they shouldn't be shocking- these failures of foresight are becoming not only increasingly common, but the norm, and there's a good reason for it- one that a fellow named Thomas Robert Malthus would have been very familiar with.

Thomas Robert Malthus, 19th century scholar and thinker. [Image source]

Malthus, in his 1798 book An Essay on the Principle of Population, was the first thinker to seriously describe the possibility and risks of overpopulation. His immediate concern was in regards to food production- he believed, not incorrectly, that global population was growing much more rapidly than food production. Food production was growing linearly as a factor of land area usage, while population was growing exponentially. He wasn't wrong on any count- the only reason we didn't hit his projected demographic catastrophe on schedule was a vast advancement in agricultural, shipping, fishing, animal husbandry, and other food-related technologies.

The unsustainable growth of humanity has continued much as he predicted, however. We're unlikely to hit a food related Malthusian crises just yet- we grow far more food than the world needs every year. World hunger is a distribution problem, not a production problem anymore. And yet, Malthus was only wrong about the nature and timeline of the problems overpopulation would cause. Ecology as a science hadn't even been invented yet, so there was no real way for him to know that the truly dangerous stresses would be ecological- nor could he predict that people would end up in more and more geologically dangerous terrain as the population of Earth grew and spread.

The eruption of Mount Vesuvius that destroyed Pompeii in CE 79, while devastating, was largely unpredictable for the Romans. We, however, are considerably more capable of predicting volcanic eruptions. Let's hope we're a lot better, because three million people live at the foot of Vesuvius today. [Image source]

A commonly heard complaint from that one archetypal uncle (who went to "the school of common sense" and believes that all poor people need is tough love) is that if people want to live near a dangerous geological feature, it's their own fault when it erupts, and we shouldn't bail them out of trouble. It's... got a certain tempting logic to it, but unfortunately for said archetypal uncle, it's also a logic devoid of real world context. There are very good reasons for living in geological hazard zones. For one, the Malthusian overpopulation crisis. We're simply low on places to live, and many of the places best suited to sustain large populations, like coastlines, tend to be geological hazard zones. Volcanoes might be dangerous, but they also make for exceptionally fertile soil.

It's not simply a matter of overpopulation forcing us into geologically hazardous or environmentally fragile regions, however. Humans overstressing a region can, and will, result in an increase in geological hazards. Clearcutting forests is one of the primary causes of landslides globally, and is a frequent consequence of human settlement in a region. It also alters the hydrology of a region drastically, and can result in significantly increased flooding.

New Orleans, Louisiana. Home to, among other things, the finest food in America. [Image source]

Take New Orleans, for example. It's a favorite topic of that crotchety old archetypal uncle from up above. "It's below sea level- we should just let it drown!" Well, apart from being one of the cultural centers of the United States, it's one of our largest ports, and a hugely disproportionate percent of the nation's heavy industry occurs along the banks of the Mississippi just upstream from it. Abandoning it would be disastrous and foolish- but there's no denying that it's also an expensive and tricky city to preserve. It's at frequent risk of flooding from storm surges- both due to a history of poor floodwater management decisions and due to the degradation of the Mississippi Delta that traditionally protected the city from storm surges- the establishment of the very levy system that protects the city from flooding has cut off much of the sediment that the delta relied on.

Los Angeles, another frequent target of our archetypal uncle character, is constantly attacked for being under threat of earthquakes. And it is true that the quakes are frequent and often destructive- but as they're slip-strike zone earthquakes, they really shouldn't be nearly so destructive. The reason they are? A history of poor building codes and construction atop landfill. (San Francisco is even worse about building on landfill.) The earthquakes, however, for all their press, are hardly the biggest threat facing Los Angeles- that would actually be debris flows. All those huge catchbasins and concrete canals in LA? They're meant to capture and deflect the frequent- and devastating- debris flows from the San Gabriel Mountains. Despite their lower profile, these debris flows are responsible for far more deaths every year than the quakes, frequently wiping out houses and even communities in the canyons of the San Gabriel. People keep moving there, however, because they're beautiful locations and because, frankly, the city does its best to not publicize the problem, and the real estate agents aren't going to mention it.

The aftermath of the 2017 Mocoa landslide in Columbia as rescuers look for survivors. Over 250 people died and 70 were left missing. It still wasn't even close to the largest landslide disaster of 2017- the Freetown landslides in Sierra Leone just five months later killed well over a thousand people. [Image source]

Unfortunately, things look like they're just going to get worse and worse from here on out. We'll be seeing more tragedies like this every year from here on out. In fact, there's a clear- and drastic- trend of increasing numbers of fatal landslides every year globally, one echoed by many other natural hazards such as disease epidemics.

We're going to be moving into a new part of this series from here on out- rather than discussing how we're using and draining the Earth's geological resources (and believe me, there are tons I didn't even address, like oil), we'll be moving on to discussing how various civilizations succeeded or failed at adapting to changing natural conditions, ecological crises, and living in hazard zones. Short version? A few have done really well, but most, not so much. Three guesses as to which type we're looking to turn out like.

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