Our world is always so complex and dynamic. We build dense populations all over the world in regions that will one day experience devastating disasters. For example just in the United States alone:
New York City, New York: Built on the delta of the Hudson River bordering the states of New York and New Jersey, New York City is built in one of the most vulnerable places in the world to wayward traveling hurricanes. It is very likely that a category 2 or stronger hurricane will strike this delta within the foreseeable future. The shape of the coast combined with the low land level of the city will allow a strong storm surge to easily overwhelm large areas of populated regions flooding causing flooding that few who live there are aware is even possible.
Miami, Florida: Build open the Eastern coast of a large ancient bed of coral, Miami stands directly in the path of angry hurricanes, but also has an unseen and seldom mentioned problem. The fresh water aquifers beneath the ground in the region are limited and take a lot of time to replenish as rain water seeps slowly through the corals. There have been two documented results of evacuating fresh water too quickly from these large underground caverns. The first is large sinkholes. The water is removed from the cavern so quickly that it can not refill fast enough naturally. With the support of the uncompressible water gone, the ground above succumbs to its own weight and collapses into the cavern creating a large hole. The other is that fresh water from rain is not abundant enough to refill the aquifer, but it is close enough to the ocean that seepage of salt water moves in to replace the missing fresh water. The result is that the drinking water supply now becomes laden with salty minerals and becomes unfit to drink.
New Orleans, Louisiana: The Big Easy is a sinking city. Built on the soft silt of the great Mississippi River delta, it continuously sinks day and night. To battle this people build extensive dike and levy systems to keep the waters of the river and the sea out of the city. This can not go on forever. As has already been proven by one devastating lady named Katrina, these man made water barriers are prone to over-topping and failure. With the fail-safe gone the large basin in which the city resides can quickly fill with water many meters in depth.
Mississippi River Valley: This area is one of the most agriculturally productive regions in the world. It is also one of the largest drainage basins in the world. When rain cell after rain cell passes over the United States, large volumes of the rain waters run into the Mississippi River basin. As it quickly fills tributaries and even the river itself it begins to flow over the banks. Because the land in the region is so flat it quickly begins to spread outwards in all directions, flooding everything for miles and miles.
Las Angeles, California: Built in one of the most clement areas in the world weather-wise, The City of Angels enjoys hundreds upon hundreds of sunny days every year along with warm temperate weather with low humidity. Unfortunately so do the extensive brush lands and forests in the nearby mountains which every year during and towards the end of the dry season generate raging wildfires which consume thousands of acres of land. These fires don't seem to have a problem devouring land with houses and buildings as they relentlessly march on looking for any and all fuel sources in their wake. Of course LA is also built on the San Andreas fault, one of the most volatile and active shear faults in the world. Recent construction codes and regulations have helped reduce the damage and death caused by even strong earth quakes, but nothing can prepare people for a mega quake in the magnitude of 8.5 or higher in the heart of a populated region. Damage and loss of life would be significant in a localized area and perhaps beyond. Then there are those rainy winter days when deluges of rain fall over the city and surrounding mountains, mountains recently stripped of ground covering vegetation by fires and people alike. The rain runs off this barren land creating flash floods of epic proportions. Crafty engineers have devised ways of handling these sudden torrents and they cause little damage. However, unseen but well known, the rain also seeps into these barren areas, many of which are located on steep hillsides or mountains. Suddenly and without warning the earth begins to flow downhill, taking everything on top with it and destroying everything in its wake. These mudslides cause massive property damage every year and often claim many lives as well.
And that is just a few places in the United States. Then there is the rest of the world. Imagine a mega tsunami caused by the sudden collapse of the Canary Islands into the Atlantic Ocean racing at 600 miles per hour towards the East coast of North America. The tsunami would strike the coast and surge inland many miles, perhaps even one hundred miles or more in flat areas. Imagine a sudden violent eruption of a super hot spot such as the enormous magma field hidden just below the surface of Yellowstone Park sending sun blocking dust and choking gases into the atmosphere around the entire globe.
Leaving our planet behind, we can look into the cosmos for even more bad news. Our own Sun, the life giver, is also a ticking time bomb. In 1989 strong solar storms nearly took the entire power grid of the Eastern United States and Canada offline. Such storms occur on an 11 year cycle, and just like hurricanes, there is no predicting when exactly they will occur or how powerful they may become. Asteroids and commets meander through the solar system like cars without drivers. There is a lot of space out there, but every now and then they bump into something with awe inspiring and devestating results.