Volcanoes have contributed significantly to the formation of the surface of our planet. Volcanism produced the crust we live on and most of the air we breathe. The remnants of an eruption reveal as much as the eruption itself, for they tell us many things about the eruption. Included here are examples of several volcanic products and other magmatic features, with descriptions of how they were formed and what they tell us about volcanism. Most volcanic rock material begins as molten rock material formed within Earth and is called magma. Eruptive products include lava (fluid rockmaterial) and pyroclastics or tephra (fragmentary solid or liquid rock material). Tephra includes volcanic ash, lapilli (fragments between 2 and 64 mm), blocks, and bombs. Perhaps the best known volcanic product is lava, the fluid rock material that flows rather quietly from volcanic vents. The external and internal structures of lava flows are the result of the physical properties of the magma from which it was derived. Of these physical properties viscosity is the most important and it is in turn affected by the temperature and chemical composition of the magma. Lavas of low viscosity can spread great distances from the vent. Greater viscosity produces thicker lava flows that generally cover less area. The rate of supply of magma relative to the velocity of the lava as it flows from the vent and the external environment through which the lava flows also affect the structure of the solidified lava. Products of explosive eruptions include pyroclastic (fire broken) rocks and rock fragments. The force that produces explosive eruptions is the release of trapped gas. Ejecta from these explosions may be derived from the magma or from rocks in the vicinity of the volcanic conduit that are blasted out in the eruption. These may be ejected more or less vertically, then fall back to earth in the form of ash fall deposits. Pyroclastic flows result when the eruptive fragments follow the contours of the volcano and surrounding terrain. They are of three main types: glowing ash clouds (nuee ardente), ash flows, and mudflows. Volcanic structures can take many forms. A few of the smaller structures built directly around vents include cinder, spatter, and lava cones. Thick lavas may pile up over their vents to form lava domes. Larger structures produced by low viscosity lava flows include lava plains. The erosion of volcanoes leaves volcanic remnants, interesting reminders of the volcano's former fury. Erosion of the layers of lava and ash that built the volcano leaves the congealed magma in the conduit. This feature, sometimes referred to as a plug or the volcanic neck or throat, is a dramatic pillar of rock rising above the surrounding plain. These plugs or necks may be composed partially of fragments of the walls of the pipe and partially of congealed magma. They may be as more than a kilometer in diameter. Magma flowing into cracks in the rocks produces dikes, sills and laccoliths. This intrusive rock is generally resistant to erosion and often remains after the surrounding rock has eroded away. These exposed intrusive rocks give us a glimpse of the complex underground network of piping in active volcanoes. These igneous features are constant reminders of the timelessness of the processes that relentlessly form, and reform, the surface of planet Earth.

The Significant Volcanic Eruptions Database is a global listing of over 600 eruptions from 4360 BC to the present. A significant eruption is classified as one that meets at least one of the following criteria: caused fatalities, caused moderate damage (approximately $1 million or more), Volcanic Explosivity Index (VEI) of 6 or greater, generated a tsunami, or was associated with a significant earthquake. The database provides information on the latitude, longitude, elevation, type of volcano, last known eruption, VEI index, and socio-economic data such as the total number of casualties, injuries, houses destroyed, and houses damaged, and $ dollage damage estimates. References, political geography, and additional comments are also provided for each eruption. If the eruption was associated with a tsunami or significant earthquake, it is flagged and linked to the related database. For a complete list of current and past activity for all volcanoes on the planet active during the last 10,000 years, please see Smithsonian Institution's Global Volcanism Program (GVP).

NCEI maintains a database of over 1,500 volcano locations obtained from the Smithsonian Institution Global Volcanism Program, Volcanoes of the World publication. The database includes information on the volcano name, location, elevation, volcano type, date of the last known eruption, and the certainty of Holocene volcanism.

Volcanic ash is a significant hazard to aviation and can also affect global climate patterns. To ensure safe navigation and monitor possible climatic impact, the NOAA Satellite Services Division (SSD) tracks volcanic ash eruptions throughout the world. After an eruption, SSD issues a Volcanic Ash Advisory (VAA) message and a forecast of ash location in the atmosphere from the Volcanic Ash Forecast Transport and Dispersion (VAFTAD) model. The Volcanic Ash Advisory Database contains VAA messages, VAFTAD model output, and substantiating information from 1983 to 2003, that have been scanned into image format. The substantiating information includes surface weather observations, pilot reports, volcanic observatory reports, news media reports, and satellite imagery for each event. This database is static and is no longer being updated by NCEI.

The word volcano is used to refer to the opening from which molten rock and gas issue from Earth's interior onto the surface, and also to the cone, hill, or mountain built up around the opening by the eruptive products. This slide set depicts explosive eruptions, lava fountains and flows, stream eruptions, and fissure eruptions from 19 volcanoes in 13 countries. Volcano types represented in this set include strato, cinder cone, complex, fissure vent, lava dome, shield, and island-forming. Perhaps no force of nature arouses more awe and wonder than that of a volcanic eruption. Volcanoes can be ruthless destroyers. Primitive people offered sacrifices to stem the tide of such eruptions and many of their legends were centered around volcanic activity. Volcanoes are also benefactors. Volcanic processes have liberated gases of the atmosphere and water in our lakes and oceans from the rocks deep beneath Earth's surface. The fertility of the soil is greatly enhanced by volcanic eruptive products. Land masses such as islands and large sections of continents may owe their existence entirely to volcanic activity. The word "volcano" is used to refer to the opening from which molten rock and gas issue from Earth's interior onto the surface, and also to the cone, hill, or mountain built up around the opening by the eruptive products. The molten rock material generated within Earth that feeds volcanoes is called magma and the storage reservoir near the surface is called the magma chamber. Eruptive products include lava (fluid rock material) and pyroclastics or tephra (fragmentary solid or liquid rock material). Tephra includes volcanic ash, lapilli (fragments between 2 and 64 mm), blocks, and bombs. Low viscosity lava can spread great distances from the vent. Higher viscosity produces thicker lava flows that cover less area. Lava may form lava lakes of fluid rock in summit craters or in pit craters on the flanks of shield volcanoes. When the lava issues vertically from a central vent or a fissure in a rhythmic, jet-like eruption, it produces a lava fountain. Pyroclastic (fire-broken) rocks and rock fragments are products of explosive eruptions. These may be ejected more or less vertically, then fall back to Earth in the form of ash fall deposits. Pyroclastic flows result when the eruptive fragments follow the contours of the volcano and surrounding terrain. They are of three main types: glowing ash clouds, ash flows, and mudflows. A glowing ash cloud (nue ardente) consists of an avalanche of incandescent volcanic fragments suspended on a cushion of air or expanding volcanic gas. This cloud forms from the collapse of a vertical ash eruption, from a directed blast, or is the result of the disintegration of a lava dome. Temperatures in the glowing cloud can reach 1,000 deg C and velocities of 150 km per hour. Ash flows resemble glowing ash clouds; however, their temperatures are much lower. Mudflows (lahars) consist of solid volcanic rock fragments held in water suspension. Some may be hot, but most occur as cold flows. They may reach speeds of 92 km per hour and extend to distances of several tens of kilometers. Large snow-covered volcanoes that erupt explosively are the principal sources of mud flows. Explosions can give rise to air shock waves and base surges. Air shock waves are generated as a result of the explosive introduction of volcanic ejecta into the atmosphere. A base surge may carry air, water, and solid debris outward from the volcano at the base of the vertical explosion column. Volcanic structures can take many forms. A few of the smaller structures built directly around vents include cinder, spatter, and lava cones. Thick lavas may pile up over their vents to form lava domes. Larger structures produced by low viscosity lava flows include lava plains and gently sloping cones known as a shield volcanoes. A stratovolcano (also known as a composite volcano) is built of successive layers of ash and lava. A volcano may consist of two

Over the last several million years the Hawaiian Islands have been built of successive lava flows. They are the most recent additions in a long line of volcanoes that extends up the intersection ofthe Aleutian Island chain with the Kamchatka peninsula. This set includes very colorful imagesof lava fountains, lakes, cascades, flows, spatter and lava entry to the sea from eruptionsoccurring over the last 30 years. Most of these volcanoes are no longer visible above the sea surface. These islands and sea mounts formed as the Pacific plate moved over a hot spot in Earth's mantle. The amount of lava that has erupted here is difficult to comprehend. Mauna Loa, on the Island of Hawaii (Big Island) is the largest volcanic structure in the world with a volume estimated at 42,000 km3. It rises from the ocean floor, 5,000 m below sea level, to a height above sea level of 4,172 meters. In addition to eruptions at the summit, Hawaiian volcanoes have flank eruptions with lavaflowing several kilometers from the vent. The height of such volcanic structures (known as shield volcanoes) increases only slightly while they continually grow in width. Hawaii's usually non-explosive eruptions are characterized by the relatively quiet outpouring of lava known as effusive eruptions. High temperature, a low gas content, and exceptionally fluid lava are typical of these eruptions. The high fluidity of Hawaiian lava comes from its basaltic composition. They are contrasted to the more viscous dacite erupted explosively at Mount Saint Helens in 1980. Hawaiian eruptions usually start with lava issuing vertically from a central vent or a fissure in a rhythmic jet-like eruption, called a lava fountain. The lava fountains vary widely in form, size and duration depending on the shape of the vent, volume of lava, and other conditions. Fountains spouting from a series of nearly continuous fissures are called curtains of fire. As the eruption proceeds the lava fountain activity is confined to a single vent or opening. The lava may form lava lakes of fluid rock in summit craters or in pit craters on the flanks of the volcanoes. If the lava lake forms around an active vent, the crust breaks up in response to circulation and sloshing of the molten lavabeneath. Lava falling from fountains and flowing from vents often forms glowing lava streams or lava flows. During some Mauna Loa eruptions flows rushed down the steep slopes at 58 km per hour. As the eruption continues, the lava solidifies along the edges of the flow building levees or ramparts that allow the level of the lava to be raised. If the roof of the channel hardens and forms a solid crust the molten lava may continue to flow within what has become a lava tube. Lava tubes generally have arched roofs but their floors may be flat, formed by the surface of the last liquid lava to move through them. The walls of such tubes become thermal insulators allowing the lava to flow greater distances from the vent. Lava streams that plunge over cliffs or the steep walls of craters form lava cascades or lava falls. There are two main types of lava flows: pahoehoe, and aa. The Hawaiian names refer to the surface character of the lava. Many flows consist ofpahoehoe upstream and change to aa downstream. However, aa flows do not change into pahoehoe. The type of lava is determined by the initial gascontent of the lava, the changes in lava viscosity and the rate of deformation (shear strain of the lava during flow and cooling). Pahoehoe has a smooth surface. In some areas it is wrinkled and twisted resembling folds in heavy cloth. This appearance results from the dragging and twisting of the thin, hot, still-plastic crust of the flow by movement of the liquid lava underneath. The surfaces of most pahoehoeflows are rolling or undulating. One can walk across a moving flow, and although the crust may bend, it does not break. The crust of a lava flow is a poor conductor of heat so the part of the flow beneath the crust may remain hot

Fewer than one hundred people have been killed by eruptions in the recorded history of Hawaii, and only one death has occurred in the 20th Century. However, the lava flows are highly destructive to populated and cultivated areas. This set depicts the negative impact of lava flows on communities, vegetation, marine life, roads, and coastlines. It also illustrates the benefits of Hawaii volcanism such as the production of geothermal power, increase in land area of the islands and other benefits. More than 270,000 people have been killed directly or indirectly by volcanic activity worldwide during the past 500 years. Nearly all of the deaths have been caused by explosive eruptions of composite volcanoes along the boundaries of the Earth's tectonic plates. Hawaii's volcanoes have more fluid, less gaseous magmas and produce quieter, less hazardous eruptions. The village of Kapoho was entirely destroyed during the 1960 eruption in the lower east rift (fissure) zone of Kilauea. In the 1980s, flows from Kilauea's east rift largely destroyed Royal Gardens and Kalapana. The March-April 1984 eruption of Mauna Loa threatened Hilo, with a population of about 40,000. Advancing nearly 26 km in about 5 days, the active flows produced a bright red glow in the night sky visible from Hilo. Much to the relief of the citizens, the flows stopped about 6.5 km short of the city's outskirts. These outskirts are built in part on the pahoehoelava (smooth ropy lava) flows produced by the 1881 eruption of Mauna Loa, indicating that Hilo is well within the reach of lava flows from the volcano. Although the destructive effects of volcanism are more obvious, volcanoes also provide many benefits to mankind. They are the major contributors to the building of continents, and all oceanic islands owe their origin directly or indirectly to volcanism. Over the billions of years of Earth's existence, water has been released from its interior by volcanoes and hot springs near volcanic intrusions. Geothermal power produced by volcanism is an inexpensive alternative energy source. The Hawaiian Islands were built over millions of years by lava flows. The lava flows have provided the fertile soil in which crops such as pineapples, sugar cane, and coffee thrive, and lush tropical vegetation flourishes. The flows start to weather quickly in areas with adequate rainfall. In some cases revegetation can begin in less than one year after the eruption. The lava flows are very fertile, especially if they have been covered by ash. The fine ash particles retain water within reach of plant roots and release plant foods such as potassium. Vegetation that has been destroyed by ash falls returns in a more luxuriant form. However in the island's arid areas, it may take thousands of years to form fertile soils from erosion and breakdown of lava. Volcanic rocks provide an abundant local source of materials for landscaping, construction, and road building. The majestic mountains andbeautiful black sand beaches of Hawaii that draw thousands of tourists each year are products of volcanism. Hawaii Volcanoes National Park provides one of the few places in the world where visitors can safely view volcanic processes. The Hawaiian volcanoes are contributing to the overall understanding of volcanoes; they provide a natural laboratory for study of the eruptivephenomena. Careful research and constant observation over long periods of time are important. From these data, volcanologists are learning to interpret activity in order to advise local officials of imminent eruptions.

Romania, an eastern European country, is severely affected by a variety of natural hazards. These include frequent earthquakes, floods, landslides, soil erosion, and drought all of which have major social and economic impacts. Thus, there is a long tradition of study of these hazards by scientific researchers in Romania. This set of slides includes examples of landslides, rockfalls,sheet erosion, and mudflows. Romania has an area of 237,500 km2 and a great variety of geologic regions. Two-thirds of the country consists of hills, tablelands, and mountains of the Carpathian arch. The climate is dominantly temperate-continental and vegetation and soils vary widely with altitude. Altitude ranges from sea level to 2,544 meters above sea level at the highest point of the Romanian Carpathians. Romania's population in 1992 was 22.76 million inhabitants, or an average density of 95.8 people per square kilometer. The Vrancea Seismic Region of the southeastern part of the Carpathian Mountains is the most active subcrustal earthquake province of Europe. The region is characterized by high seismicity, with about three major earthquakes greater than magnitude (M) 7.0 occurring every century. The best studied earthquake of recent times occurred March 4, 1977, and had a magnitude of 7.2. This earthquake caused the death of 1,570 people, and destroyed 33,000 buildings. In addition to earthquakes, torrential rains are responsible for catastrophic floods, massive landslides, and major soil erosion. Mass movements are a significant hazard in the hilly and mountainous regions, particularly those underlain by flysch deposits. These deposits are complexes of folded and faulted sedimentary rocks containing marls, clays, shales, sandstones, and conglomerates. The distribution of mass movements in these deposits is controlled by various climatic, tectonic, and lithologic factors influenced by different land-management practices. There are significant regional differences among types of mass movements, the quantities of materials delivered from the slopes into adjacent stream channels, and risks to various human activities. In the Subcarpathians, formed predominantly of folded and faulted molasse deposits, slopes may be highly unstable. The instability is most frequently manifested by shallow (sheet) slides, landslides of medium depth, and mudflows typically 300-700 meters in length. The areas most affected by these features lie within the Curvature Subcarpathians in the Vrancea Seismic Region. In the Eastern Carpathians, formed predominantly of Cretaceous and Paleocene flysch deposits, periglacial or immediate postglacial colluvial materials are major sources of mass movements. These deposits generally range from 10 to 30 meters in depth, and landslides within them arecommonly activated or reactivated by regional deepening of the valley network in the long term, or deforestation practices by people. Because oftheir association with stream valleys, these landslides often affect towns, communication lines, and roads, and may partially or totally block valleys when they move. In the Moldlavian Plateau, the areas most affected by landslides occur on slopes built up of alternations of marls and clays, with intercalations of conglomerates and sandstones. In the Transylvanian Plateau deep landslides called "glimee" are commonly triggered by heavy rains. In the alpine belt of the Carpathian mountains, the most common mass movements are rockfalls and rock avalanches. These processes are mostcommon in the crystalline rocks on the steep slopes of glacial cirques and valleys. Sheet and gully erosion affect most of the hilly and mountainous regions of Romania. Agricultural lands on slopes steeper than 5% represent 42% ofthese regions and contribute to the bulk of sheet and gully erosion. About 20% of the agricultural lands are affected by high to very high erosionrates of 8-16 T/HA/year; 19% are subject to more moderate rates of 2-8 T/HA/Year; and about 3% are