10 Formidable Ways the Earth Can Turn Dangerous Suddenly

The Earth does not always announce danger with a smoking volcano, a darkening funnel cloud, or an approaching hurricane. Some threats develop beneath ordinary streets, inside peaceful mountain lakes, or within soil that appears perfectly solid. By the time the landscape visibly changes, the process responsible may already be well underway.

Many of these phenomena are secondary hazards, created when familiar natural forces interact in unexpected ways. A thunderstorm can generate a moving wall of dust. An earthquake can weaken the ground or accidentally build a dam. A collapsing glacier can turn a tranquil lake into a destructive flood.

Some of these hazards are rare, while others occur regularly in vulnerable regions. What connects them is their capacity to transform a familiar landscape with remarkable speed. The following documented events demonstrate ten bizarre ways the Earth can suddenly become dangerous.

Related: Ten Astonishing Ways That the Earth Is Evolving

10 Sinkholes Can Open in Hours

A sinkhole can make the ground beneath a road, house, or parking lot appear perfectly normal—right up until it suddenly is not. These depressions are most common where groundwater can dissolve limestone, gypsum, salt, or other soluble rock. As the rock disappears, it leaves cavities and weakened areas beneath the surface.

Not every sinkhole forms in the same way. Some develop slowly as loose material settles into openings below. The more alarming variety is the cover-collapse sinkhole, which forms when a layer of clay-rich sediment temporarily bridges an underground cavity. The concealed roof can hold for a while and then fail rapidly, sometimes within hours.

Rainfall, drought, leaking pipes, construction, and changes in groundwater levels can all affect the process. Pumping large quantities of groundwater can be particularly dangerous because it removes some of the support beneath overlying sediment.

That happened near Dover, Florida, during a severe freeze in January 2010. Farmers pumped groundwater to protect crops, causing the water table to fall to record-low levels. More than 110 sinkholes subsequently appeared, damaging homes, roads, and cultivated land. What looked like a stable landscape had been relying partly on water that was suddenly no longer there.^[1]

9 Haboobs Can Swallow a Landscape in Minutes

The original idea of a “mud storm” is more accurately described as a haboob: a vast wall of airborne dust generated by powerful thunderstorm winds. When cool air rushes downward from a storm and spreads across dry ground, it can lift enormous quantities of loose soil into the atmosphere.

The resulting cloud may stretch for miles and rise thousands of feet. From a distance, it can resemble a solid brown wall moving across the landscape. Once it arrives, daylight may fade, and visibility can collapse to almost nothing within minutes. The combination of strong wind and blinding dust makes haboobs especially hazardous for drivers.

One extraordinary example struck south-central Arizona on July 5, 2011. Thunderstorm outflows produced a dust front nearly 100 miles (160 kilometers) across at its widest point. The cloud reached an estimated height of at least 5,000 to 6,000 feet (1,500 to 1,800 meters) and traveled at least 150 miles (240 kilometers).

The haboob crossed the entire Phoenix metropolitan area, producing widespread reports of zero visibility and wind gusts exceeding 50 mph (80 km/h). Road traffic stopped, flights at Phoenix Sky Harbor International Airport were suspended for 45 minutes, and the city was left coated in dust. An ordinary monsoon thunderstorm had effectively created a fast-moving land-based blackout.^[2]

8 Earthquakes Can Make Solid Ground Lose Its Strength

During an earthquake, the greatest danger does not always come from buildings shaking. In areas with loose, waterlogged soil, the ground itself can temporarily lose much of its strength and behave more like a fluid. This process is known as liquefaction.

Normally, sand and silt grains press against one another and support the weight above them. Strong shaking increases the pressure of the water between those grains, pushing them apart and reducing the friction that holds the soil together. The ground has not literally melted, but it may no longer support buildings, roads, or bridges.

Structures can tilt or sink, buried pipes and tanks may float upward, and the surface can split or spread sideways. Water and sand may also erupt through cracks, creating features known as sand boils. Because the vulnerable soil can look entirely ordinary before an earthquake, the risk is easy to overlook.

During the 1989 Loma Prieta earthquake in California, liquefaction affected soil and debris that had been used to fill a former lagoon beneath San Francisco’s Marina District. The ground subsided, fractured, and slid horizontally, contributing to severe damage in a neighborhood located more than 60 miles (97 kilometers) from the earthquake’s epicenter.^[3]

7 Glacial Lakes Can Burst Their Natural Dams

High in mountainous regions, melting glaciers can create lakes held back by ice, loose rock, or ridges of sediment known as moraines. These natural barriers may remain intact for decades, giving the lake an appearance of permanence. However, they are not engineered dams, and their failure can release an enormous volume of water with little warning.

A glacial lake outburst flood, often abbreviated as GLOF, can begin when an avalanche, rockfall, or collapsing section of glacier plunges into the lake. The impact may generate a wave that overtops the natural dam. Water flowing across the barrier then erodes it, enlarging the opening and releasing the lake even faster.

The flood does not remain clear water for long. As it races through a narrow valley, it can pick up boulders, mud, trees, and ice, becoming a dense debris flow that can destroy structures far downstream.

On August 4, 1985, Nepal’s Dig Tsho glacial lake burst after an ice avalanche fell into the water. The resulting flood destroyed the nearly completed Namche Small Hydroelectric Project and damaged downstream bridges, trails, homes, and farmland. The disaster demonstrated how an event beginning in a remote glacial basin can suddenly threaten communities many miles away.^[4]

6 Earthquakes Can Build Dangerous Dams

An earthquake can alter a river without breaking the ground directly beneath it. Strong shaking may dislodge millions of tons of rock and soil from a mountainside, sending the material into a narrow valley. If enough debris reaches the bottom, it can block the river and create a new lake.

The sudden appearance of this natural dam produces two different threats. Water backing up behind the blockage can inundate upstream communities, roads, and farmland. Meanwhile, people downstream face the possibility that the loosely packed dam will erode or collapse.

Some landslide dams survive for years, but others fail within hours or days. Water may seep through the debris, cut a channel across its surface, or overtop it completely. Once erosion begins, the opening can enlarge rapidly, releasing the stored lake as a violent flood loaded with sediment and boulders.

The magnitude 7.6 Kashmir earthquake of October 8, 2005, produced a striking example near Hattian Bala in Pakistan-administered Kashmir. A vast rock avalanche destroyed a village, blocked two tributaries of the Jhelum River, and created new lakes behind the debris. Although the earthquake lasted only moments, the dam and its accumulating water created a separate hazard that required years of monitoring and intervention.^[5]

5 Lahars Can Race Far Beyond a Volcano

A volcanic eruption does not have to bury a town in lava to destroy it. Lahars—fast-moving mixtures of water, volcanic ash, rock, and other debris—can pour into river valleys and travel far beyond the volcano itself.

Some lahars begin when an eruption rapidly melts snow or glacial ice. Others form when heavy rain remobilizes loose volcanic material, so the danger can continue long after the eruption ends. As the flow moves downhill, it collects additional sediment, trees, vehicles, and pieces of buildings. The result can resemble wet concrete moving with the force of a flash flood.

One of history’s deadliest lahars followed the November 13, 1985, eruption of Colombia’s glacier-covered Nevado del Ruiz. The eruption was relatively small, but its heat melted part of the mountain’s ice. Lahars raced through surrounding river valleys toward settlements that could not see the volcano.

Approximately two hours later, a lahar reached Armero, located about 28 miles (45 kilometers) from the summit. Within minutes, the town was buried beneath mud, vegetation, wreckage, and volcanic debris. Approximately 23,000 people in Armero were killed. The distant eruption had transformed an ordinary river valley into the route for a disaster.^[6]

4 Rogue Waves Can Rise from an Ordinary Sea

For centuries, sailors described enormous walls of water appearing without warning in the open ocean. People often dismissed their accounts as exaggerations. Scientists now know rogue waves are real, although predicting exactly when and where they will appear remains difficult.

A rogue wave is generally defined as one measuring more than twice the height of the surrounding waves. It is not simply the largest wave in a storm. It is a sudden outlier that may approach from an unexpected direction, with steep sides and an unusually deep trough in front of it.

Several processes can create one. Waves traveling at different speeds or from different directions may briefly align, allowing their energy to combine through constructive interference. Strong ocean currents moving against waves can also compress them and focus their energy. The towering result may last only minutes before disappearing back into the surrounding sea.

One rogue wave photographed in the Gulf Stream off Charleston, South Carolina, was estimated to be 60 feet (18.3 meters) high. Surface winds measured only about 15 knots, making the wave dramatically larger than the conditions seemed capable of producing. It struck a ship moments before the photograph was taken—a stark demonstration that an ocean does not have to look exceptionally violent to produce an exceptional wave.^[7]

3 A Landslide Can Throw Water Up a Mountainside

Tsunamis are usually associated with earthquakes beneath the ocean, but a collapsing mountainside can generate an even more extreme local wave. When millions of tons of rock suddenly plunge into a lake, reservoir, or narrow fjord, the falling material displaces the water almost instantaneously.

Unlike an ocean-crossing tsunami, a landslide-generated wave may strike nearby shores before any warning can be issued. Narrow bodies of water surrounded by steep terrain are especially vulnerable because the landscape can concentrate the displaced water rather than allowing it to spread outward.

The most dramatic documented example occurred at Alaska’s Lituya Bay on July 9, 1958. An earthquake triggered a massive rockslide at the head of the narrow bay. When the rock struck the water, it generated a wave that surged across the inlet and up the opposite mountainside.

The wave stripped trees and soil from the slopes to a maximum elevation of 1,720 feet (524 meters)—higher than the Empire State Building. It also scoured the shoreline as far as 3,600 feet (1,097 meters) inland, carried one fishing boat over a spit of land, and sank another. A geological collapse lasting moments had forced seawater to heights normally reached only by clouds.^[8]

2 Permafrost Can Explode into Giant Craters

In 2014, researchers discovered an enormous crater in the frozen ground of Siberia’s Yamal Peninsula. Its shape and the debris scattered around it suggested that something beneath the permafrost had exploded. Researchers later identified additional craters on the Yamal Peninsula and nearby peninsulas.

Researchers found unusually high methane concentrations at the first crater. Methane can exist underground in ice-like structures called methane hydrates, which remain stable under low temperatures and high pressure. Siberian permafrost also contains cryopegs—unfrozen pockets of extremely salty water buried beneath the seasonally thawed surface.

One recent model proposes that meltwater is drawn toward a cryopeg by osmotic pressure. As more water enters, pressure builds inside the confined pocket until the surrounding frozen soil fractures. That sudden pressure loss can destabilize nearby methane hydrates, releasing gas rapidly enough to produce a violent physical explosion.

Before an explosion, the swelling ground may form a mound that resembles a pingo, a more familiar ice-cored hill. The surface can therefore look merely uneven until the pressure beneath it becomes too great. Although these explosions appear rare and confined to unusual geological conditions, they show that seemingly permanent frozen ground can conceal a pressurized system that can blast open without warning.^[9]

1 A Lake Can Release an Invisible Killing Cloud

A deep lake can store far more than water. In rare volcanic settings, carbon dioxide seeps upward from beneath the ground and dissolves in the cold water at the lake’s bottom. The tremendous pressure at that depth allows the water to hold more gas.

If the lake’s layers become disturbed, some of the gas-rich water may rise. Lower pressure lets carbon dioxide form bubbles, much like a carbonated drink foaming after it is opened. Those bubbles pull more deep water upward, potentially causing a runaway release known as a limnic eruption.

The escaping carbon dioxide is invisible and denser than ordinary air. Instead of dispersing upward immediately, it can flow downhill through valleys and settlements, displacing the breathable air near the ground. Victims may lose consciousness without ever seeing, smelling, or hearing the danger approach.

On the night of August 21, 1986, Cameroon’s Lake Nyos suddenly released a massive quantity of carbon dioxide. The gas spread into nearby villages and killed approximately 1,700 people, many while they slept. Hundreds of survivors required medical treatment, and thousands of livestock also died. There was no lava, ash cloud, or approaching wall of water—only a peaceful-looking lake releasing an invisible atmosphere that people could not breathe.^[10]