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At least 199 records · Page 11Linked to original sources
USGS1986

Meteoroids and impact craters

On a clear night scores of meteoroids streak across the sky. they leave light paths we call meteors or shooting stars as the Earth is showered with debris from distant parts of the solar system. When these meteoroids hit the Earth (as meteorites) they range in size from pebbles to the 34 ton Ahnighito meteorite that the American explorer Admiral Robert Peary discovered in Greenland. The unique importance of meteorites is that they have an extra-terrestrial origin and can provide us with direct evidence on the make-up of the solar system. They also give us clues to the origin of the solar system because they formed about 4.6 billion years ago at about the time the planets formed. Many meteoroids are associted with comets; as a comet travels around the sun it leaves a trail of debris behind it and it is this debris which produces meteor showers. Other meteoroids come from the asteroid belt, a zone between Mars and Jupiter filled with thousands of dwarf worlds that failed to coalesce into planets.

Earthquakes & Volcanoes (USGS)↗
USGS1986

New theories about ancient extinctions

The abrupt disappearance of all the dinosaurs about 65 million years ago, along with perhaps half the plant species and other animals, has been one of the great geological mysteries. Clues to the cause of these extinctions have been scarce and open to many interpretations. But all this may be changing. Mass extinctions have been very much in the news in the last few years, triggered in large part by the proposal that the extinction of the dinosaurs and marine animals was caused by a catastrophic collision between the Earth and an extra-terrestrial body (bolide). Recently an equally contentious suggestion has been made that mass extinctions have swept the Earth every 26 to 31 million years for at least the last 250 million years-caused by encounters with some kind of extra-terrestrial object such as one of the asteroids or the comets.

Earthquakes & Volcanoes (USGS)↗
USGS1986

The Tunguska comet or the great Siberian mystery explosion of 1908

It is dawn on a June morning in Siberia in 1908. The sky is cloudless, but even in summer this part of Russia the cold at dawn takes your breath away. Fur-clad nomads are beginning to herd their sheep and goats towards lush grazing on the banks of the river-one of the thousands that drift sluggishly across Siberia's vast featureless wilderness towards the Arctic Ocean. Swans glide in the dark shallows of the river. A phalanx of ducks spears into a nearby swamp and sends up a black cloud of ferocious mosquitoes; they settle again around a herd of reindeer browsing on the river bank. Here where the tiaga, the forbidding Siberia forest, obscures the sun, the cold is a sharp as the flint in the river bed. It cuts the farmer who has just emerged from his log cabin. He halts on the steps to decide whether this first task of the day will be to mend the plough that was broken yesterday when he dug too deep and reached permanently frozen ground, or whether he will hunt for rabbit for the evening meal; instead he lights his pipe. Two families of nomads are still asleep in their tents, the air strong with the scent of wet dog as the ice melts on their furs. At a trading post, trappers squabble over the price of ermine and sable pelts. On the edge of the settlement a tramp with pots and pans jingling on his back sets off on his day's journey to the nearest village, twenty miles away. At the edge of the village, a boatman pushes off from the river bank for his first crossing of the day, the crescent-shaped hull of his boat overloaded with squawking chickens, snarling dogs and silent peasants. Without warning there is a blinding blue flash in the sky, followed by a roar and a searing blast of heat; there is a thunderous clap, the ground shudders, and this air is filled with fire, black smoke and debris. The boat disintegrates, hurling men and animals into the freezing river. The farmer's shirt is scorched off his back; the tramp is blown off his feet, his ports and pans scattering like shrapnel. One of the trappers standing in the doorway of the trading post is knocked unconscious, overcome by the searing heat; the tents of the nomads are torn loose, the men and dogs inside being rolled over the ground like leaves in a gale. All that remain of the reindeer are charred carcasses. The forest has been turning into a crackling inferno, and a black fireball rises into the air.

Earthquakes & Volcanoes (USGS)↗
USGS1987

An interview with Bruce A. Bolt

Professor Bruce Bolt was educated in Australia and first came to the United States in 1960 on a Fulbright Fellowship to the Lamont Geological Observatory of Columbia University. In 1963 he was appointed Director of the Seismographic Stations at the University of California at Berkeley. In June 1988, he steps down as Director but his association will continue as Professor of Seismology. Henry Spall interviewed him again 10 years after a 977 interview published in the Earthquake Information Bulletin.

Earthquakes & Volcanoes (USGS)↗
USGS1989

Measuring the size of an earthquake

Earthquakes range broadly in size. A rock-burst in an Idaho silver mine may involve the fracture of 1 meter of rock; the 1965 Rat Island earthquake in the Aleutian arc involved a 650-kilometer length of the Earth's crust. Earthquakes can be even smaller and even larger. If an earthquake is felt or causes perceptible surface damage, then its intensity of shaking can be subjectively estimated. But many large earthquakes occur in oceanic areas or at great focal depths and are either simply not felt or their felt pattern does not really indicate their true size. Today, state-of-the-art seismic systems transmit data from the seismograph via telephone line and satellite directly to a central digital computer. A preliminary location, depth-of-focus, and magntidue can now be obtained within minutes of the onset of an earthquake. The only limiting factor is how long the seismic wave stake to travel from the epicenter to the stations-usually less than 10 minutes.

Earthquakes & Volcanoes (USGS)↗
USGS1990

National Earthquake Hazards Reduction Program; time to expand

All of us in earthquake engineering, seismology, and many related disciplines have been directly or indirectly affected by the National Earthquake Hazards Reduction Program (NEHRP). This program was the result of the Earthquake Hazards Reduction Act of 1977 (Public Law 95-124). With well over a decade of experience, should this expression of public policy now take a different or expanded role?

Earthquakes & Volcanoes (USGS)↗
USGS1991

The volcanic record that gets away

Volcanologists are accustomed to looking at the record in the rocks to read volcanic history. They map the extent of airfalls, the thickness and distribution of ignimrites and mudflows, and the nature and extent of lava flows. From these data they infer the story of previous eruptive episodes that are a key to what we may expect in the future. BUt some important volcanic events are not recorded. Without observations at present-day active volcanoes we would know little about the volcanic gas emitted, the kidns of gases, or the volume and the extent o the gas cloud.

Earthquakes & Volcanoes (USGS)↗
USGS1990

Volcano hazard mitigation program in Indonesia

Volcanological investigations in Indonesia were started in the 18th century, when Valentijn in 1726 prepared a chronological report of the eruption of Banda Api volcno, Maluku. Modern and intensive volcanological studies did not begin until the catastrophic eruption of Kelut volcano, East Java, in 1919. The eruption took 5,011 lives and destroyed thousands of acres of coffee plantation. An eruption lahar generated by the crater lake water mixed with volcanic eruptions products was the cause of death for a high number of victims. An effort to mitigate the danger from volcanic eruption was first initiated in 1921 by constructing a tunnel to drain the crater lake water of Kelut volcano. At the same time a Volcanological Survey was established by the government with the responsibility of seeking every means for minimizing the hazard caused by volcanic eruption.

Earthquakes & Volcanoes (USGS)↗
USGS1993

Volcanic gases create air pollution on the Island of Hawai’i

In a handful of molten magma weighing about a pound, there is less than a tenth of an ounce, by weight, of idssolved gas-roughly the same weight as a pinch of table salt. Yet this tiny amount of gas produces spectacular lava foundations hundreds of meters high (see accompanying photograph). The fountain occurs as magma reaches the surface, because dissolved volcanic gases exolve and expand tremendously as pressure on the magma is released. Anyone who has shaken a bottle of soda and opened it quickly has received the full value of this basic principle of physics. Gases are dissolved in magma at depth, where pressures within Earth's crust are very great-many thousands of pounds per square inch. As the magma rises to the surface and erupts, the pressure decreases, and gas is released. The main gases dissolved in magma are water vapor, carbon dioxide, and sulfur gases, with lesser amounts of others, such as hydrogen, carbon monoxide, hydrochloric acid, and hydrofluoric acid. In our pinch-of-salt-to-a-handful-of-magma illustration above, most of the "pinch" is water vapor, followed by lesser amounts of carbon dioxide and sulfur gases with a few "grains" of hydrogen and other acid gases. The current eruption of Kilauea produces large quantities of volcanic gases that contribute to "volcanic air pollution." In this article we discuss the nature of the gases released from Kilauea, hoe we study them, and what happened to the gases in the environment after they are released.

Hawaii↗
USGS1991

Volcanologists and the geologic past

Were volcanologists to be asked why they study active volcanoes, they would list many reasons: to understand their dynamics, to use them as windows into the earth, to warn of hazards, to provide nearly real-time information on rates of various physical and chemical processes, and many others. Near the bottom of the list would be "to understand the Earth's past." Generally, that task has been left to other corners of the earth sciences, and volcanologists have kept their sights on the present or near present without worrying much about what happened millions of years ago. But much can be gained from applying a volcanologic perspective to the interpretation of old rocks, and this gain enhances our understanding of both the past and the present.

Earthquakes & Volcanoes (USGS)↗
USGS1993

Seismic detection of tornadoes

Tornadoes represent the most violent of all forms of atmospheric storms, each year resulting in hundreds of millions of dollars in property damage and approximately one hundred fatalities. In recent years, considerable success has been achieved in detecting tornadic storms by means of Doppler radar. However, radar systems cannot determine when a tornado is actually in contact with the ground, expect possibly at extremely close range. At the present time, human observation is the only truly reliable way of knowing that a tornado is actually on the ground. However, considerable evidence exists indicating that a tornado in contact with the ground produces a significant seismic signal. If such signals are generated, the seismic detection and warning of an imminent tornado can become a distinct possibility.

Earthquakes & Volcanoes (USGS)↗
USGS1988

Scientific goals of the Parkfield earthquake prediction experiment

Several unique circumstances of the Parkfield experiment provide unprecedented opportunities for significant advances in understanding the mechanics of earthquakes. to our knowledge, there is no other seismic zone anywhere where the time, place, and magnitude of an impending earthquake are specified as precisely. Moreover, the epicentral region is located on continental crust, is readily accessible, and can support a range of dense monitoring networks that are sited either on or very close to the expected rupture surface. As a result, the networks located at Parkfield are several orders of magnitude more sensitive than any previously deployed for monitoring earthquake precursors (a preearthquake change in strain, seismicity, and other geophysical parameters). In this respect the design of the Parkfield experiment resembles the rationale for constructing a new, more powerful nuclear particle accelerator:in both cases increased capabilities will test existing theories, reveal new phenomena, and suggest new research directions.

Earthquakes & Volcanoes (USGS)↗
USGS1990

Perspectives on earthquake hazards in the New Madrid seismic zone, Missouri

A sequence of three great earthquakes struck the Central United States during the winter of 1811-1812 in the area of New Madrid, Missouri. they are considered to be the greatest earthquakes in the conterminous U.S because they were felt and caused damage at far greater distances than any other earthquakes in U.S history. The large population currently living within the damage area of these earthquakes means that widespread destruction and loss of life is likely if the sequence were repeated. In contrast to California, where the earthquakes are felt frequently, the damaging earthquakes that have occurred in the Easter U.S-in 155 (Cape Ann, Mass.), 1811-12 (New Madrid, Mo.), 1886 (Charleston S.C) ,and 1897 (Giles County, Va.- are generally regarded as only historical phenomena (fig. 1). The social memory of these earthquakes no longer exists. A fundamental problem in the Eastern U.S, therefore, is that the earthquake hazard is not generally considered today in land-use and civic planning. This article offers perspectives on the earthquake hazard of the New Madrid seismic zone through discussions of the geology of the Mississippi Embayment, the historical earthquakes that have occurred there, the earthquake risk, and the "tools" that geoscientists have to study the region. The so-called earthquake hazard is defined by the characterization of the physical attributes of the geological structures that cause earthquakes, the estimation of the recurrence times of the earthquakes, the estimation of the recurrence times of the earthquakes, their potential size, and the expected ground motions. the term "earthquake risk," on the other hand, refers to aspects of the expected damage to manmade strctures and to lifelines as a result of the earthquake hazard.

New Madrid seismic zone↗
USGS1993

The October 12, 1992, Dahshur, Egypt, Earthquake

Cairo and northeastern Egypt experienced a rare, damaging earthquake on October 12, 1992. The earthquake, which measured 5.9 on the Richter magnitude scale, was centered near the village of Dahshur, about 18 km south of Cairo. The computed hypocentral depth of the earthquake, about 25 km, is consistent with the fact that fault rupture associated with the earthquake did not reach the surface. Despite its relatively moderate size, the earthquake caused many casualties and heavy damage. These losses included more than 500 fatalities, more than 6,500 injuries, and about 8,300 damaged or destroyed buildings. The Foreign Broadcast Service estimated monetary losses directly attributable to the earthquake at $300 million. We were part of an international reconnaissance team that investigated the Dahsur earthquake. This article summarizes our findings and points out how even a relatively moderate sized earthquake can cause widespread damage and a large number of casualities.

Earthquakes & Volcanoes (USGS)↗
USGS1990

Coping with volcanic hazards; a global perspective

Compared to some other natural hazards-such as floods, storms, earthquakes, landslides- volcanic hazards strike infrequently. However, in populated areas , even very small eruptions can wreak havoc and cause widespread devastation. For example, the 13 November 1985 eruption of Nevado del Ruiz in Colombia ejected only about 3 percent of the volume of ash produced during the 18 May 1980 eruption of Mount St. Helens. Yet, the mudflows triggered by this tiny eruption killed more than 25,000 people.

Earthquakes & Volcanoes (USGS)↗
USGS1991

Reducing volcanic risk; are we winning some battles but losing the war?

Historically, significant advances in volcanology have been catalyzed by volcanic disasters or crises, reflecting the the simple fact that volcanoes seem to receive serious scientific and public attention only when they cause, or threaten to cause, trouble. For example, three deadly eruptions in 1902, Mount Pelee, Santa Maria, and Soufriere (St.Vincent), spurred the movement to establish permanent volcano observatories there. Profoundly impresses by the devastation cused by Mont Pelee, Thomas A. Jaggar, Jr. founded the Hawaiian Volcano Observatory (HVO) in 1912. Since then, studies conducted at HVO and new observatories have been pivotal in transforming the nascent science of volcanology into the multidisciplinary science that it is today.

Earthquakes & Volcanoes (USGS)↗