About the SA Blog Network

Guest Blog

Guest Blog

Commentary invited by editors of Scientific American
Guest Blog HomeAboutContact

Why we live in dangerous places

The views expressed are those of the author and are not necessarily those of Scientific American.

Email   PrintPrint

Natural disasters always seem to strike in the worst places. The Sendai earthquake has caused over 8,000 deaths, destroyed 450,000 people’s homes, crippled four nuclear reactors and wreaked over $300 billion in damage. And it’s only the latest disaster. Haiti will need decades to rebuild after its earthquake. New Orleans still hasn’t repopulated following Hurricane Katrina. Indonesia still feels the effect of the 2004 tsunami. The list could go on and on. The unfortunate lesson is that we live in dangerous places.

We have built civilization’s cornerstones on amorphous, impermanent stuff. Coasts, rivers, deltas and earthquake zones are places of dramatic upheaval. Shorelines are constantly being rewritten. Rivers fussily overtop their banks and reroute themselves. With one hand, earthquakes open the earth, and with the other they send it coursing down hillsides. We settled those places for good reason. What makes them attractive is the same thing that makes them dangerous. Periodic disruption and change is the progenitor of diversity, stability and abundance. Where there is disaster, there is also opportunity. Ecologists call it the “intermediate disturbance hypothesis.”

The intermediate disturbance hypothesis is one answer to an existential ecological question: Why are there so many different types of plants and animals? The term was first coined by Joseph Connell, a professor at UC Santa Barbara, in 1978.¹ Connell studied tropical forests and coral reefs, and during the course of his work, he noticed something peculiar. The places with the highest diversity of species were not the most stable. In fact, the most stable and least disturbed locations had relatively low biodiversity. The same was true of the places that suffered constant upheaval. But there, in the middle, was a level of disturbance that was just right. Not too frequent or too harsh, but also not too sparing or too light. Occasional disturbances that inflict moderate damage are, ecologically speaking, a good thing.

To see how this works, let’s imagine a hypothetical forest, one that escapes disturbance for thousands, even millions of years. Eventually, it will be dominated by two species—a tree species that is best adapted to the type of soil, quantity of water and amount of sunlight, and an understory species that can best cope with limited sunlight under the canopy. No other species could possibly compete; eventually, two species would become the best plants for the conditions. While it’s a gross generalization, it illustrates the point. Stable environments can stifle diversity.

This would not be the case in a more realistic forest, however, one that suffers from the periodic fallen tree, occasional fire or odd tornado. In the window opened by disturbances, other species would have ample opportunity to gain a foothold. If a tree falls, other species could bolt toward the sun. After a fire, herbs that sprout vigorously would have a leg up on previously dominant plants that bud languorously. Life explodes into the openings when given new opportunities.

Biodiversity has flourished where the occasional disturbance kicks open a door. These places are also all the more stable for it. Diversity breeds stability. They are also richer in food and resources, two qualities that attracted our ancestors. The natural bounty of those places made the occasional hurricane or tsunami tolerable.

Today, many of us don’t have the same problems our forebears did. We don’t need to live next to our food. Our water comes from a tap. We can drop our packages off at the post office. But the past is hard to escape. While the requirements of the last century may have disappeared, our cities have not. We are creatures of habit.

Yet social inertia is not the only reason we still live in dangerous places. As aesthetically tuned creatures, we crave dramatic landscapes forged by catastrophe. California is celebrated for its tectonic rocky shores. Mount Saint Helens almost certainly has more visitors now than before it blew its top. The Mississippi River is responsible for untold hardship, yet it’s held up as an honored piece of Americana.

That’s not to say that the Sendai earthquake or Australia’s Black Saturday bushfires will be lauded in the future. They are more than intermediate disturbances—they are real disasters. Yet in ecological terms, each would have been a small speed bump. What turns intermediate disturbances into natural disasters is population density. Earthquakes didn’t kill when our buildings didn’t require stairs. And though tsunamis still have always been devastating, they caused few human casualties before we built cities. Avalanches in remote parts of Alaska don’t usually raise eyebrows, but they are a constant concern for many villages in the Swiss Alps. Much of the handwringing over sea level rise is precisely because so much of the world’s population lives near the ocean.

That’s not to say we should flee the coasts or abandon the breathtaking but dangerous places. Our fear of change may seem like a hindrance, but our stubbornness is also one of our greatest assets. Without overcoming intermediate disturbances like floods or sandstorms, there would be no Rome or Cairo. We live on a tumultuous planet where life has thrived under a regime of constant upheaval. Adapting is—and always has been—our last, best hope.

¹ Though he coined the term, two previous studies had described essentially the same concept.


Connell, J.H. 1978. Diversity in tropical rain forests and coral reefs. Science 199(4335):1302-10. PMID: 17840770

Wilkinson, D.M. 1999. The Disturbing History of Intermediate Disturbance. Oikos 84(1):145-147. DOI: 10.2307/3546874.


The Great Wave off Kanagawa by Hokusai. Source: Library of Congress via Wikipedia.

About the Author: Tim De Chant is the creator of Per Square Mile, a blog about density, and a contributor to Ars Technica. He received his PhD in Environmental Science, Policy and Management from the University of California, Berkeley and was a AAAS Mass Media Fellow at the Chicago Tribune. You can find him on Twitter at @tdechant and on the web at

The views expressed are those of the author and are not necessarily those of Scientific American.


Comments 15 Comments

Add Comment
  1. 1. BlakeJustBlake 7:58 pm 03/28/2011

    I don’t think this really aptly explains "why we live in dangerous places." Examining various marginal areas with high diversity will reveal mainly plants that, through the eyes of those who live near and use the area, are considered weeds. The kinds of plants that humans actually eat, compared to the number of species that one finds, is pretty small. So, I suppose one would have a better chance of finding something edible in a largely diverse area, but it’s not exactly a given like you seem to assume. At least if there is a relationship between higher diversity and a more common presence of stuff humans would want to eat you might want to provide some sort of source from that, because as much as that sounds nice I can’t just believe it off hand.

    Perhaps the answer to why we live in dangerous places is something that would easier be explained when looking into why we live anywhere at all. I couldn’t say for certain, but I believe it’s hard to actually find large expanses of land on earth that could be considered consistently safe for humans to live. I would say this is partially because the main reason we can really survive in such vast areas is due to cultural adaptations. So I would say that we live in these areas, for one, out of necessity. I wouldn’t go and say that biodiversity doesn’t play any part in it at all, but I believe there is a lot more to it, especially a lot more than it being aesthetically pleasing. One should probably look at all factors in each case of a "dangerous" place, because I’m sure there’s much more to it than diversity of plants.

    Link to this
  2. 2. Bora Zivkovic 8:15 pm 03/28/2011

    I am not sure how the trait "usefulness to humans" is relevant to the ecological analogy (or metaphor) of this post.

    Link to this
  3. 3. outsidethebox 8:59 pm 03/28/2011

    The answer can be summed up in one word: economics.

    Link to this
  4. 4. jtdwyer 10:33 pm 03/28/2011

    The article states:
    "Today, many of us don’t have the same problems our forebears did. We don’t need to live next to our food. Our water comes from a tap. We can drop our packages off at the post office. But the past is hard to escape. While the requirements of the last century may have disappeared, our cities have not. We are creatures of habit."

    I don’t find this argument to be very compelling. International trade and shipping has become economically critical, now that we have outsourced our manufacturing overseas. Much of our food still comes from the seashore (until seafood is depleted). Most of our drinking water comes from the tap because of urban potable water infrastructure, not to mention waste processing (nobody likes to mention that).

    People still chose to live in cities by the seashore primarily because of available functional infrastructure and economic opportunity. We do like to live as comfortably as possible, but we do not chose our home sites based on periodic opportunity produced by disastrous turmoil. We chose to live in dangerous locations because we assess our short term need fulfillment to exceed our long term risks.

    By the way, I understand that Californians are amazed that Midwesterners expose themselves to those devastating tornadoes, while Midwesterners expect California to fall into the sea. Go figure…

    Link to this
  5. 5. eco-steve 4:52 am 03/29/2011

    People soon forget after natural disasters, which generally occur ,say, every 200 years. Also religeous people are fatalist, as they believe such disasters are an act of God, which can be avoided through prayer.
    Whilst such primitive belief systems hold sway, massive human catastrophes will continue. Scientists have been advising planners for well over a century not to build in safety critical zones. But corruption prevails.

    Link to this
  6. 6. mike cook 11:37 am 03/29/2011

    My angle on this has been to try to figure out a safe place to live. Presently my wife and I live near Seattle but way above tsunami level and I have retrofitted the foundation tie-downs for earthquake safety. The house could still come down so in every room there is a survival saw, an axe, and some water storage. In the garage and basement I have a collection of jacks and cribbing.

    Fortunately, Mt. Rainier is not a supervolcano. When it blows it will be a spectacular show but we can sit on our deck and be spectators. I am concerned about two large, sharp edged obsidian rocks I have found buried in my sandy gravel yard that must have been blown there by a volcanic eruption as they show no sign of stream polishing whatsoever.

    I would choose West Texas near a dependable reservoir as my next best bet, as that area is further away from the expected Yellowstone extinction level event and other than tornados, wildfires, and some drug trafficker problems has no huge intrinsic hazards. I am predicting a suddent onset little ice age so I want to get far enough south that a new planting zone will have a long enough season to grow enough to eat.

    Link to this
  7. 7. jgrosay 4:40 am 03/30/2011

    As Saint Paul said: "please let us live a decent, honest, peaceful life". Salut +

    Link to this
  8. 8. bobandpat 4:31 pm 03/30/2011

    I can understand the economic reasons people take risk with where they live. The biodiversity thing is interesting, and I suppose it says something about who we are – maybe those who live at risk are more likely to be inventive.
    But what I don’t get is why people go back to the same flood prone river valley locations time after time when they don’t have to. We call them idiots, but then we cry for them and bail them out again when the next flood comes. Are they the dumb ones? Or is it us?

    Link to this
  9. 9. mike cook 5:03 pm 03/30/2011

    We have to understand that humans are born to survive. It may seem counter-intuitive, but a lot of times survival involves taking considerable risks. No risk-avoider ever killed a mammoth with a sharp stick or climbed on a rotten, leaking 16th century ship bound for the new world because her owners thought it might have one good profitable crossing left in it, if it avoided storms.

    Link to this
  10. 10. Laird Wilcox 6:43 pm 03/30/2011

    Perhaps the question is framed incorrectly. "Why do dangerous places occur where people live?" would be more to the point. No one says, "Hey, this place is dangerous. Let’s live here." Although animal rights groups may disagree, absent people, the places would not be dangerous. The point that stairs make earthquakes dangerous is also incorrect. It is not stairs but height. A few stairs barely increases danger at all, but many stairs is another issue entirely. To put it another way, the risk from falling is directly related to how high one is. The only time we really need to be near our food is when we eat it but I understand research is being undertaken to change that. The best place to be during a disaster is somewhere else and I always try to be somewhere else in the first place. This really isn’t too hard to think through.

    Link to this
  11. 11. Quinn the Eskimo 8:39 pm 03/30/2011

    Ummmm. Okay, where IS it safe to live?

    Kansas? New York City? Detroit? South Central? Nagasaki?

    Link to this
  12. 12. briseboy 3:37 pm 03/31/2011

    Well written by many commentators!

    Ecotones: where different ecosystems overlap. In those areas exist far greater species diversity.
    Diversity due to the larger number of niches – let’s call them resources – extant in the marginal areas. This certainly can be regarded as more dangerous to most species, and this contributes to the reason there are more niches.

    Pacific shores can be regarded as more tsunamically dangerous due to the collision of tectonic plates causing subsidence, pressures; the movement is inhibited by massive frictions that is only relieved when the pressure is increased enough to overcome them.

    Looking at active fault zones, we find they occur largely in areas affecting tropical and temperate areas. Humans have proliferated to occupy all these areas intensively.
    Tsu-nami means harbor wave. Like classic bores, (hope I’m not one!) harbors and shallowing bottoms funnel long, low waves into short, high ones. This is why when first seeing a tidal wave as an adolescent, I said:"the tide goes out, the tide comes in." Just faster, higher, and lower than normal.
    Harbors are useful to humans for protection from storm and wind waves; thus they became trade centers.
    Before pavement and machine road grading, it was always far cheaper and easier to use waterways for trade and travel.

    Water surfaces are always near water tables, except in such isolated cases as huecos or tanks: water underlain by impermeable rock.
    River basins are always replenished with soil by periodic inundation, and so agriculturalists could continue settlement there beyond a very few years.

    Periodic disturbance occurs in all ecosystems.

    The earth constantly cycles in geologic processes that create analogues to ecotones.

    By terming portions of these cycles, "disasters", whether we mean weather, subcrustal melting, evaporation, pressure release, we word-creators merely artificially isolate portions of a continuous process. Organisms inhabiting ever-changing ecosystems ALWAYS encounter changes that reduce their niche, or enlarge it.

    Only one of the commentors pretends to permanence, worrying about "safety" and where to live to achieve it. This artifact of the human psyche, called imagination, is a significant problem when overblown. Japan experiences a massive washover of urban and agricultural areas, while citizens of the US are concerned with fictive possibilities and probable events.

    There are forces and events larger than any human constructs. We are mortal. Science studies, we apply these. New challenges evolve. The last word is key.

    Link to this
  13. 13. Briansz 2:40 am 04/4/2011

    Some people like the Japanese have no choice to live in potentially dangerous place like Islands in Japan. Contrary to narcissistic North Americans who live in potentially dangerous places for the view and the real estate value.

    Link to this
  14. 14. atomfullerene 11:23 pm 04/5/2011

    I’m not sure I buy that we live in dangerous places because they are dangerous. I think the danger is just a side effect of the characteristics that we really want. For instance: we live in areas that flood because flooded soils are fertile, and large rivers (which produce larger floods) are better for transporting freight. Deep, narrow bays make better harbors…and concentrate tsunamis. Volcanic soil often is enriched with nutrients. Coasts provide transport and fish for protein. The occasional hurricane doesn’t outweigh this-but it doesn’t cause it either.

    Link to this
  15. 15. bucketofsquid 9:51 am 04/6/2011

    I am amazed at the lack of reading comprehension of many of the posters responding to this blog post. Most of the objectors don’t address his conclusions or evidence at all, simply ignoring what they don’t like and using this forum to promote their own religious/political agendas. I do think the author is a little weak on one of the main reasons life, including us humans; continue to occupy dangerous areas is that they tend to be the most fertile. Volcanic areas and areas prone to flooding have some of the most fertile soil in the world. Coastlines have access to seafood.

    Link to this

Add a Comment
You must sign in or register as a member to submit a comment.

More from Scientific American

Email this Article