Damage was extensive and large as twenty-five miles of the San Andreas Fault slipped.

On October 18, 1989, an earthquake of magnitude 6.9 struck a branch fault of the San Andreas near the city of Santa Cruz in the southern Santa Cruz Mountains. It came to be known as the Loma Prieta earthquake after the name of a 3,000-foot mountain in the Santa Cruz area that was close to the epicenter. A series of thousands of destructive landslides was triggered all along a stretch of coast and in the central valley from north of San Francisco to points forty-five miles south of Santa Cruz. This earthquake took sixty-three lives, cost $10 billion, and damaged 27,000 structures. The source of the quake was a slip along a twenty-five-mile segment of the San Andreas Fault where it crosses the Santa Cruz Mountains sixty miles south of San Francisco. It was the most powerful earthquake to strike this part of California since the 1906 San Francisco quake.

Extensive studies were made in the wake of this quake to ensure adequate preparation for any future similar event. For the most part, places that were damaged by landslides were checked out and where necessary, as in some coastal locations, homes were removed or other remedial action taken. One particularly weak area was the Marina District of San Francisco. Despite the experience of 1906 when this part suffered severe damage, city officials went on to fill the area with sand and rubble from the quake, in order to use it as a site for the 1912 Panama–Pacific International Exhibition. In later years it became a very popular section of the city. The lurking danger, which was ignored, was liquefaction in the event of an earthquake. When Loma Prieta struck, the Marina area immediately sunk five inches. This was followed by widespread liquefaction as water saturated sand turned into a liquid. Buildings shifted off their foundations and many collapsed.

Thousands of landslides generated by the quake were found all over an area half the size of the one hit in 1906. Loma Prieta thus provided the first opportunity to study the effects of a major earthquake on landslides. Previous landslide-producing earthquakes, apart from the 1906 quake, were either too small or too poorly documented for this purpose. Techniques for identifying slopes susceptible to failure that had been developed over the previous ten years were proved correct in the studies that followed the Loma Prieta earthquake. At the same time there was recognition of new types of landslide hazards not fully appreciated in the past. The most severe property damage occurred in San Francisco and Oakland. The earthquake was felt over most of central California and in part of western Nevada.

It was fortunate that the epicenter was in a sparsely populated area because the amount of shaking was very strong. In homes furniture was moved several feet and in one case a built-in oven was ejected from its cabinet. The city of Watsonville was badly damaged as were older buildings in downtown Santa Cruz. Around the margins of San Francisco Bay the shaking that was experienced in 1906 was much stronger than in 1989. Most publicity was focused on the collapse of a section of the freeway that connects downtown Oakland to the Bay Bridge. The freeway’s bridge was built in 1936 and was intended to withstand moderate earthquakes. Such designs were common at that time before people were acquainted with the damaging influence of earthquake motions.

This was the second largest volcanic eruption worldwide in the twentieth century. The biggest was Mount Katmai in Alaska in 1912.

On June 15, 1991, and persisting for eight hours, the second largest volcanic eruption of the twentieth century, that of Mount Pinatubo, took place on the island of Luzon in the Philippines. The largest eruption was Katmai in Alaska in 1912. Pinatubo is only fifty-five miles from the capital city, Manila. As many as eight hundred people were killed and 100,000 became homeless following the eruption. Millions of tons of sulfur dioxide were discharged into the atmosphere, causing a decrease in the surface temperature of the entire globe over the next few years.

Mount Pinatubo is part of a chain of volcanoes along the Luzon arc on the west coast of the main island of the Philippines, Luzon, created by subduction action of tectonic plates similar to the way the volcanic mountains of Cascadia develop, such as Mount St. Helens. The events of the 1991 eruption began back in July 1990, when a magnitude 7.8 earthquake occurred sixty-two miles northeast of the Pinatubo region, a result of the reawakening of Mount Pinatubo. In mid-March 1991, villagers around Mount Pinatubo began feeling earthquakes and volcanologists began to study the mountain. About 30,000 people lived in villages on the flanks of the volcano prior to the disaster. On April 2, 1991, small explosions from the mountain led to eruptions of ash that was deposited on local villages. The first evacuations of 5,000 people were ordered later that month.

Before the catastrophic eruption of 1991, Pinatubo was not a dominant landmark, unknown to most people in the surrounding areas. Its summit was 5,725 feet above sea level, but only about 1,800 feet above nearby plains, and only about six hundred feet higher than surrounding peaks, which largely obscured it from view. An indigenous people, the Aeta, had lived on its slopes and in surrounding areas for several centuries, having fled the lowlands to escape persecution by the Spanish. They were a hunter-gatherer people who were extremely successful in surviving in the dense jungles of the area. The dense jungle that covered most of the mountain and surrounding peaks supported the hunter-gathering Aeta, while on the surrounding low-lying areas the abundant rainfall provided by the monsoon climate and the fertile volcanic soils provided excellent conditions for agriculture. Many people grew rice and other staple foods. Many of the Aeta who lived on the slopes of the volcano left their villages of their own volition when the first explosions began in April, gathering in a village about eight miles from the summit. They moved to increasingly distant villages as the eruptions escalated, some moving as much as nine times in the two months preceding the eruption.

Earthquakes and explosions continued to occur. On June 5, a level 3 alert was issued for two weeks due to the possibility of a major eruption. The extrusion of a lava dome on June 7, led to the issuance of a level 5 alert on June 9, indicating an eruption in progress. An evacuation area twelve miles away from the volcano was established and 25,000 people were evacuated. On June 10, Clark Air Base, a U.S. military installation near the volcano, was evacuated. The 18,000 personnel and their families were transported to Subic Bay Naval Station and most were returned to the United States. On June 12, the danger radius was extended to eighteen miles from the volcano and this involved increasing the total numbers evacuated to 58,000. Unfortunately, at the time of the eruption, Tropical Storm Yunya was passing forty-seven miles to the northeast of Mount Pinatubo, causing a large amount of rainfall in the region. The ash that was ejected from the volcano mixed with the water vapor in the air to cause deposits of rock and ash to fall across the whole of the island of Luzon. Many of the eight hundred people who died during the eruption were killed by the weight of the ash collapsing roofs and killing occupants. Had Tropical Storm Yunya not been nearby, the death toll from the volcano would have been much lower.

The volcano had experienced major eruptions in the past, the last being about five hundred years ago. Pinatubo stood about 5,725 feet above sea level before the June 1991 eruption. On June 15, the climactic eruption of Mount Pinatubo began in the early afternoon and lasted for nine hours, causing numerous earthquakes due to the collapse of the summit of Mount Pinatubo and the creation of a caldera. The caldera reduced the peak from 5,725 feet to 4,872 feet. In addition to the ash, Mount Pinatubo ejected between fifteen and thirty million tons of sulfur dioxide gas. Sulfur dioxide in the atmosphere mixes with water and oxygen in the atmosphere to become sulfuric acid, which in turn triggers ozone depletion. Over 90 percent of the material released from the volcano was ejected during the nine-hour eruption of June 15. The human impacts of the disaster are staggering. In addition to the up to eight hundred people who lost their lives, there was almost one half of a billion dollars in property and economic damage. The economy of central Luzon was completely disrupted, the volcano having destroyed 4,979 homes and damaged another 70,257. One year after the eruption thousands of additional homes were destroyed and 3,137 were damaged, usually as a result of rain-induced torrents of volcanic debris.

The eruption plume of Mount Pinatubo’s various gasses and ash reached high into the atmosphere within two hours of the eruption, reaching an altitude of twenty-one miles and covering an area 250 miles wide. This eruption was the largest disturbance of the stratosphere since the eruption of Krakatau in 1883. It had a Volcanic Explosivity Index (VEI) of 6, making it equivalent to some of the most violent eruptions in all of human history. Mount Vesuvius, Krakatau, and Thera of ancient Greece all had VEI of 6. The aerosol cloud spread around the earth in two weeks and covered the planet within a year. During 1992 and 1993, as a result of this aerosol cloud, the ozone hole over Antarctica reached an unprecedented size, creating a heightened risk of skin cancer all over the world. The cloud over the earth reduced global temperatures. In 1992 and 1993, the average temperature in the Northern Hemisphere was greatly reduced and the entire planet experienced its minimum temperature in August 1992.

Overall, the cooling effects of Mount Pinatubo’s eruption were greater than those of the El Nino climatic event that coincided with the aftermath of the eruption. Pinatubo’s cooling effects were also much greater in the years 1992 and 1993 than the increases that were accumulating due to human actions via greenhouse gases. The United States military never returned to Clark Air Base. The damaged base was turned over to the Philippine government on November 26, 1991. In all, the eruption ejected about two and a half cubic miles of material into the atmosphere. Damage to health care facilities, and the spread of illnesses in relocation facilities, led to soaring death rates in the months following the eruption. Education for thousands of children was seriously disrupted by the destruction of schools in the eruption.

The peak gusts of 164 mph led to huge destruction of homes in the built-up area of southern Florida. Total damage costs were $26.5 billion.

Hurricane Andrew was the most destructive twentieth century U.S. hurricane. It reached Florida as a category 4 storm where it made landfall at Homestead at 5 A.M. on August 24 with a peak gust of 164 mph. It caused twenty-three deaths in the United States, three more in the Bahamas, and ended up with a damage total of $26.5 billion, of which $1 billion occurred in Louisiana. The vast majority of the damage in Florida was due to the winds.

This most destructive hurricane started modestly as a tropical wave that emerged from the west coast of Africa on August 14. The wave spawned a tropical depression on August 16, which became Tropical Storm Andrew the next day. Further development was slow, as the west-northwestward moving Andrew encountered an unfavorable upper-level trough. Indeed, the storm almost dissipated on August 20 due to vertical wind shear. By August 21, Andrew was midway between Bermuda and Puerto Rico and turning westward into a more favorable environment. Rapid strengthening occurred, with Andrew reaching hurricane strength on August 22 and category 4 status on August 24 when it made landfall in Florida.

Florida is no stranger to hurricanes and throughout the twentieth century, again and again, the frequency and strength of the storms that arrived led to the waxing and waning of its attractiveness to northerners who wanted to enjoy its warmer temperatures. In the forty years from 1926 to 1966, Miami was hit with hurricanes about thirteen times but from the quarter century 1966 to 1992 there were none and during that period of time people flocked to Miami, doubling its population. New subdivisions sprung up but supervision of building codes and other regulations was lax. There were fewer than twenty building inspectors for a population of one million. The sudden arrival of Andrew was a great shock. Its fierce winds caused most of the damage. Houses were torn apart, cars lifted off the streets, and trees uprooted. Boarding up their windows proved useless as a protection in the face of the wind and very few homes had basements where people could shelter. It was an almost total destruction of whole subdivisions.

Reports from private barometers helped establish that Andrew’s central pressure at landfall in Homestead, Florida, was 27.23 inches, which makes it the third most intense hurricane of record to hit the United States. Andrew’s peak winds in south Florida were not directly measured due to the official measuring instruments having been destroyed. A storm surge of seventeen feet was recorded at Homestead. Thereafter the hurricane continued westward into the Gulf of Mexico where it gradually turned northward. This motion brought Andrew to the central Louisiana coast on August 26 as a category 3 hurricane where the storm surge of eight feet inundated much of the Louisiana coast. It also triggered a killer tornado in southeastern Louisiana. The storm then turned northeastward, eventually merging with a frontal system over the mid-Atlantic on August 28.

In all, 63,000 of the residences in Dale County, where Miami is located, were destroyed and another 110,000 damaged. Nine out of every ten mobile homes were also destroyed. Hospitals, fire stations, and other emergency stations had been put out of action by the storm and relief was slow to arrive from other places because there were no telephones or other communications to contact them. Andrew remained the most devastating natural disaster in U.S. history until the arrival of Hurricane Katrina in 2005. The name Andrew was retired in the spring of 1993 and will never again be used for an Atlantic hurricane. It was replaced with Alex in the 1998 season.

The damage caused was enormous and concentrated because this earthquake occurred within a densely-populated area.

An earthquake of magnitude 6.7 hit an area of high population density twenty-five miles northwest of Los Angeles at 4:30 A.M. on January 17, 1994. About ten million people in the Greater Los Angeles region felt the impact of the quake. This earthquake, named for its epicenter in the town of Northridge, proved to be the costliest in U.S. history. Communities throughout the San Fernando Valley and in its surrounding mountains north and west of Los Angeles were affected, causing losses of 20 billion dollars. Fifty-seven people died, more than 9,000 were injured, and more than 20,000 were displaced from their homes.

Because the earthquake was centered beneath a built-up urban area, the impact on buildings of all kinds was immense. Thousands of buildings were significantly damaged, and more than 1,600 became unsafe to enter. The shaking lasted for less than thirty seconds but in that time buildings came down, freeway interchanges collapsed, and fires broke out as gas lines were broken. Fortunately, the early morning timing of the earthquake spared many lives that otherwise might have been lost in collapsed parking buildings and on failed freeways. Freeway bridges built or designed before the mid-1970s and had not been retrofitted to meet new standards failed. Telephone systems broke down, not because of equipment failure but due to overload and they were inadequate for an emergency of this scale.

The earthquake began as a rupture on a hidden fault at a depth of ten miles beneath the San Fernando Valley. For eight seconds following the initial break, the rupture continued to extend upward and northwestward along the fault plane at a rate of two miles per second. The rupture front spread out across as well as along the fault plane, so that the eventual size of the rupture covered an area of ten by twelve miles. The rupture stopped at a depth of three miles. Maximum intensities from the quake were felt in and near Northridge and in Sherman Oaks. Lesser, but still significant intensities were felt in Fillmore, Glendale, Santa Clarita, Santa Monica, Simi Valley, and in western and central Los Angeles. A rise in ground level of six inches occurred in the Santa Susana Mountains and there were many rockslides in mountain areas that blocked roads. Some ground cracks were observed at Granada Hills and liquefaction occurred at a number of locations in the Simi Valley.

In summary, all the lifeline systems in the areas affected by the quake were damaged in various ways, including freeways, communications, gas, water, power, and sewage. Additionally, the delivery of water from the Colorado River and northern California was disrupted so that some areas were without water for weeks. This earthquake measured 6.7 on the Richter Scale and there is a tendency to assume that an event of this strength will do less damage than one of magnitude 8 or higher. However, everything changes when an earthquake occurs in the middle of a major urban area. In Japan in 1995, when the city of Kobe was hit with a quake of magnitude 6.9, the destruction that followed was far costlier than anything the country had previously experienced. Costs in that event were seven times the total for the Northridge quake.

Like the Northridge earthquake that also occurred in a densely populated area, Kobe suffered very extensive damage and many casualties.

Early in the morning of January 17, 1995, Kobe, Japan, experienced the nation’s most destructive earthquake since 1946. Its epicenter was at Awaji, offshore from Kobe, and ten miles below the surface. Damage was extensive and there were many casualties. Over 5,400 were killed, another 26,800 injured, and over 300,000 made homeless. Additionally, around 105,000 buildings were damaged beyond repair and numerous others suffered lesser forms of damage. The financial costs of the earthquake were in excess of 150 billion U.S. dollars.

The Kobe area is dominated by the Philippine Tectonic Plate’s sub ducting action as it moves beneath the Eurasian Plate at a rate of about two inches a year. Great subduction earthquakes arise from this action at average recurrence rates of one hundred years. This part of Japan has the densest number of faults of anywhere in the country and they, like the main sub ducting action, also on average have an annual slippage rate, one much smaller than that of the main tectonic plate. As a result of these lesser fault movements, the Kyoto-Osaka corridor has experienced more intraplate earthquakes throughout history than any other region of Japan.

The quake devastated central Kobe, crushing buildings and homes and filling the narrow streets with debris. Train services, so vital to Japan’s transportation system, came to a sudden stop and all electricity and water provisions were cut off. So complete was the destruction of everything that the term “Great Hanshin Disaster” was born to indicate an event similar to the “Great Kanto Disaster” of 1923. The word “Hanshin” is another term for the Kobe Region. With the loss of all water supplies it became impossible to cope with all the fires that broke out as electrical sparks and flammable materials were thrown together. Thus a firestorm, like the one that engulfed San Francisco in 1906 for the same reason, and lack of water supplies, swept across Kobe. By late on January 17, there were 234 fires and, before the middle of the next day, five hundred conflagrations were consuming the large amounts of flammable materials that lay around.

The destruction that took place along Kobe’s waterfront was another mirror image of the 1906 earthquake, that of liquefaction. All along the waterfront zone of Kobe extensive reclamation work had gone on for decades to provide space for shipping activities and warehouses. The widespread liquefaction that took place destroyed the roads leading to the waterfront installations, collapsed both housing and warehouses, and lowered the ground level across the whole area by several feet. A few buildings that had been erected on deeper geological formations remained intact. Liquefaction extended downward in the reclaimed areas as deep as thirty feet in the wake of the thousands of aftershocks that followed the main quake and the wave movements in these deeper zones of liquefaction damaged several areas farther inland.

Minimum amounts of restoration took several months to complete. Gas and electrical supply lines had been so badly disrupted that even Japan’s extremely efficient system of records was incapable of deciding what line belongs where. Officials had to interview individual family survivors, mass media reports, and a variety of telephone and printed records before reconnecting trunk lines. For water lines, the available pressure was initially inadequate for identifying breaks in the system and when officials tried to reach locations to examine conditions directly they were held up by a total absence of roads. Within the downtown part of Kobe all the main streets were impassable. Removing liquefied sand from damaged pipes was yet another hurdle to overcome before the pipes could be reconnected.

This international waterway annually faces the risk of flooding because of the several variables that affect water levels in both countries.

The Red River Flood of 1997, affecting both the United States and Canada, was a major flood that occurred in May 1997 in North Dakota, Minnesota, and southern Manitoba. It was the most severe flood of the river since 1826, causing extensive flooding and destruction on both sides of the border and damaging almost $3 billion worth of property. The Red River originates in Minnesota and flows northward through a large glacial lake basin, that of Lake Agassiz, the largest of the glacial lakes that were formed at the close of the last ice age. It covered an area of half a million square miles and left in its wake a low-lying landscape, almost completely flat in places. The Red River overflows its banks in most years and the low elevation of the surrounding terrain ensures that water covers a big area when that happens. The flatness of the river basin is evident in the gradient as the river flows northward, an average slope of six inches per mile for the whole five hundred miles of its length. Natural levees, five feet in height, rise on either side of the river.

The events of 1997 were far worse than anything previously experienced. The river reached the cities of Grand Forks and East Grand Forks, where floodwaters stretched outwards from the river for three miles, inundating virtually everything in these two cities and causing US$2 billion in damages. The situation was similar in Canada.

Floods are notoriously unpredictable as the Chinese discovered over the centuries of their history and as the United States discovered with the Mississippi River. In fact, our inability to distinguish between weather and climate in our preoccupation with the advancing global warming has tended to make us attribute every daily change in temperature or precipitation to global warming. Media commentators are worst culprits here. The last time that Winnipeg had a flood like that in 1997 was 1826 and Canadian meteorologists predicted that it would not repeat for a further five hundred years. It came back in about 170 years.

There was some sense of imminent threat in Grand Forks but the National Weather Service (NWS) had a long-standing forecast for the river to crest at forty-nine feet, the river’s highest level during the 1979 flood, so people felt secure. The cities had been able to get their dikes to this level, but the river continued to rise past it in 1997, to the astonishment of the NWS that had failed to upgrade its forecast until April 16, 1997, the day the river actually reached forty-nine feet. The dikes over Grand Forks and East Grand Forks area all were overtopped on that day, flooding thousands of homes, and necessitating the evacuation of all of East Grand Forks and 75 percent of Grand Forks. School was cancelled in both cities for the remainder of the term, as were classes at the University of North Dakota.

Because all transportation was cut off between the two cities, East Grand Forks residents were evacuated to nearby Crookston, namely to the University of Minnesota, Crookston, while residents of Grand Forks went to the Grand Forks Air Force Base. Many residents also evacuated to motels and homes in neighboring communities. The river crested at 54.35 feet on April 21, 1997, and the river level would not fall below forty-nine feet until April 26 of that same year. Because water drained so slowly out of the most low-lying areas, some homeowners couldn’t visit their damaged property until May. There was $2 billion USD in damage to Grand Forks and East Grand Forks. Grand Forks lost 3 percent of its population from 1997 to 2000 and didn’t fare as badly as its sister city which lost nearly 17 percent of its residents. The five-foot discrepancy between the actual crest and that which the NWS had predicted led to widespread anger among locals, especially since the citizens of both cities reached and even slightly surpassed the NWS’s level of protection through weeks of hard work while raising the level of the dikes.

The province of Manitoba completed the Red River Floodway in 1968 after six years of excavation, put up permanent dikes in eight towns south of Winnipeg, and built clay dikes and diversion dams in the Winnipeg area. However, even with these flood protection measures, the province was not prepared for the 1997 event, known as “The Flood of the Century.” At the flood’s peak in Canada on May 4, the Red River occupied an area of nine hundred square miles with more than a thousand additional square miles of land under water, appropriately named the red sea. There were 75,000 people who had to abandon their homes. Damage costs were $450 million. The U.S.–Canadian Mission that looked after the Red River Waterway immediately began to plan for better protection against floods.

In retrospect, there were five main factors that contributed to the flood’s severity: (1) rainstorms in autumn of 1996 had saturated the ground so that it could not absorb much water; (2) there was overabundant snowfall during the 1996–1997 winter; (3) an abnormally cold temperature regime plagued the Upper Midwest during this same winter; (4) between November 7 of 1996 and March 18 of 1997 the air temperature reached forty degrees for three days only so there was very little melting of the snow; (5) a freak blizzard dumped a large amount of snow on the area on the weekend of April 5, 1997.