Mid-Atlantic Ridge above sea level at Iceland A geologically young land, Iceland is located on both the Iceland hotspot and the Mid-Atlantic Ridge, which runs right through it. This location means that the island is highly geologically active with many volcanoes, notably Hekla, Eldgjá, Herðubreið and Eldfell.

Iceland has many geysers, including Geysir, from which the English word is derived, and the famous Strokkur, which erupts every 5–10 minutes. After a phase of inactivity, Geysir started erupting again after a series of earthquakes in 2000. Geysir has since then grown quieter and does not erupt often.

With the widespread availability of geothermal power, and the harnessing of many rivers and waterfalls for hydroelectricity, most residents have access to inexpensive hot water, heating and electricity. The island itself is composed primarily of basalt, a low-silica lava associated with effusive volcanism as has occurred also in Hawaii. Iceland, however, has a variety of volcanic types (composite and fissure), many producing more evolved lavas such as rhyolite and andesite. Iceland has hundreds of volcanoes within approx. 30 volcanic systems active

Surtsey, one of the youngest islands in the world, is part of Iceland. Named after Surtr, it rose above the ocean in a series of volcanic eruptions between 8 November 1963 and 5 June 1968. Only scientists researching the growth of new life are allowed to visit the island.

On 21 March 2010, a volcano in Eyjafjallajökull in the south of Iceland erupted for the first time since 1821, forcing 600 people to flee their homes. Further eruptions on 14 April forced hundreds of people to abandon their homes. The resultant cloud of volcanic ash brought major disruption to air travel across Europe.

Another large eruption occurred on 21 May 2011. This time it was the Grímsvötn volcano, located under the thick ice of Europe’s largest glacier, Vatnajökull. Grímsvötn is one of Iceland’s most active volcanoes and this eruption was much more powerful than the 2010 Eyjafjallajökull activity. The eruption hurled ash and lava 20 km (12.43 mi) up into the atmosphere, creating a large cloud that for a while was thought to pose a danger to jet aircraft over a wide area of northern Europe.

Volcanology of Iceland

The Appalachian Mountains , often called the Appalachians, are a system of mountains in eastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period, and once reached elevations similar to those of the Alps and the Rocky Mountains before they were eroded. The Appalachian chain is a barrier to east-west travel as it forms a series of alternating ridgelines and valleys oriented in opposition to any road running east-west.

Definitions vary on the precise boundaries of the Appalachians. The United States Geological Survey (USGS) defines the Appalachian Highlands physiographic division as consisting of thirteen provinces: the Atlantic Coast Uplands, Eastern Newfoundland Atlantic, Maritime Acadian Highlands, Maritime Plain, Notre Dame and Mégantic Mountains, Western Newfoundland Mountains, Piedmont, Blue Ridge, Valley and Ridge, Saint Lawrence Valley, Appalachian Plateaus, New England province, and the Adirondack provinces. A common variant definition does not include the Adirondack Mountains, which geologically belong to the Grenville Orogeny and have a different geological history to the rest of the Appalachians.

Overview

The range is mostly located in the United States but extends into southeastern Canada, forming a zone from 100 to 300 mi (160 to 480 km) wide, running from the island of Newfoundland 1,500 mi (2,400 km) southwestward to Central Alabama in the United States. The range covers parts of the islands of Saint Pierre and Miquelon, which comprise an overseas territory of France. The system is divided into a series of ranges, with the individual mountains averaging around 3,000 ft (910 m). The highest of the group is Mount Mitchell in North Carolina at 6,684 feet (2,037 m), which is the highest point in the United States east of the Mississippi River.

The term Appalachian refers to several different regions associated with the mountain range. Most broadly, it refers to the entire mountain range with its surrounding hills and the dissected plateau region. However, the term is often used more restrictively to refer to regions in the central and southern Appalachian Mountains, usually including areas in the states of Kentucky, Tennessee, Virginia, Maryland, West Virginia, and North Carolina, as well as sometimes extending as far south as northern Georgia and western South Carolina, as far north as Pennsylvania and southern Ohio.

The Ouachita Mountains in Arkansas and Oklahoma were originally part of the Appalachians as well, but became disconnected through geologic history.

Geology of the Appalachians

Geological history

Paleozoic Era

During the earliest Paleozoic Era, the continent that would later become North America straddled the equator. The Appalachian region was a passive plate margin, not unlike today’s Atlantic Coastal Plain Province. During this interval, the region was periodically submerged beneath shallow seas. Thick layers of sediment and carbonate rock were deposited on the shallow sea bottom when the region was submerged. When seas receded, terrestrial sedimentary deposits and erosion dominated.

During the middle Ordovician Period (about 480-440 million years ago), a change in plate motions set the stage for the first Paleozoic mountain building event (Taconic orogeny) in North America. The once quiet Appalachian passive margin changed to a very active plate boundary when a neighboring oceanic plate, the Iapetus, collided with and began sinking beneath the North American craton. With the creation of this new subduction zone, the early Appalachians were born.

Along the continental margin, volcanoes grew, coincident with the initiation of subduction. Thrust faulting uplifted and warped older sedimentary rock laid down on the passive margin. As mountains rose, erosion began to wear them down. Streams carried rock debris downslope to be deposited in nearby lowlands.

This was just the first of a series of mountain building plate collisions that contributed to the formation of the Appalachians. Mountain building continued periodically throughout the next 250 million years (Caledonian, Acadian, Ouachita, Hercynian, and Allegheny orogenies). Continent after continent was thrust and sutured onto the North American craton as the Pangean supercontinent began to take shape. Microplates, smaller bits of crust, too small to be called continents, were swept in, one by one, to be welded to the growing mass.

By about 300 million years ago (Pennsylvanian Period) Africa was approaching the North American craton. The collisional belt spread into the Ozark-Ouachita region and through the Marathon Mountains area of Texas. Continent vs. continent collision raised the Appalachian-Ouachita chain to a lofty mountain range on the scale of the present-day Himalaya. The massive bulk of Pangea was completed near the end of the Paleozoic Era (Permian Period) when Africa (Gondwana) plowed into the continental agglomeration, with the Appalachian-Ouachita mountains near the core.

Mesozoic Era and later

Pangea began to break up about 220 million years ago, in the Early Mesozoic Era (Late Triassic Period). As Pangea rifted apart a new passive tectonic margin was born and the forces that created the Appalachian, Ouachita, and Marathon Mountains were stilled. Weathering and erosion prevailed, and the mountains began to wear away.

By the end of the Mesozoic Era, the Appalachian Mountains had been eroded to an almost flat plain. It was not until the region was uplifted during the Cenozoic Era that the distinctive topography of the present formed. Uplift rejuvenated the streams, which rapidly responded by cutting downward into the ancient bedrock. Some streams flowed along weak layers that define the folds and faults created many millions of years earlier. Other streams downcut so rapidly that they cut right across the resistant folded rocks of the mountain core, carving canyons across rock layers and geologic structures.

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Plate Tectonics Map
Plate Boundary Map

Note : The above story is reprinted from materials provided by Wikipedia
Plate Boundary By : USGS 

The Cascade Volcanoes (also known as the Cascade Volcanic Arc or the Cascade Arc) are a number of volcanoes in a volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern California, a distance of well over 700 mi (1,100 km). The arc has formed due to subduction along the Cascadia subduction zone. Although taking its name from the Cascade Range, this term is a geologic grouping rather than a geographic one, and the Cascade Volcanoes extend north into the Coast Mountains, past the Fraser River which is the northward limit of the Cascade Range proper.

Some of the major cities along the length of the arc include Portland, Seattle, and Vancouver, and the population in the region exceeds 10,000,000. All could be potentially affected by volcanic activity and great subduction-zone earthquakes along the arc. Because the population of the Pacific Northwest is rapidly increasing, the Cascade volcanoes are some of the most dangerous, due to their past eruptive history, potential eruptions and because they are underlain by weak, hydrothermally altered volcanic rocks that are susceptible to failure. Mount Rainier is one of the Decade Volcanoes due to the danger it poses to Seattle and Tacoma. Many large, long-runout landslides originating on Cascade volcanoes have inundated valleys tens of kilometers from their sources, and some of the inundated areas now support large populations.

The Cascade Volcanoes are part of the Pacific Ring of Fire, the ring of volcanoes and associated mountains around the Pacific Ocean. All of the known historic eruptions in the contiguous United States have been from the Cascade Volcanoes. Two most recent were Lassen Peak in 1914 to 1921 and a major eruption of Mount St. Helens in 1980. It is also the site of Canada’s most recent major eruption about 2,350 years ago at the Mount Meager volcanic complex.

Geology

The Cascade Arc includes nearly 20 major volcanoes, among a total of over 4,000 separate volcanic vents including numerous stratovolcanoes, shield volcanoes, lava domes, and cinder cones, along with a few isolated examples of rarer volcanic forms such as tuyas. Volcanism in the arc began about 37 million years ago, however, most of the present-day Cascade

volcanoes are less than 2,000,000 years old, and the highest peaks are less than 100,000 years old. Twelve volcanoes in the arc are over 10,000 ft (3,000 m) in elevation, and the two highest, Mount Rainier and Mount Shasta, exceed 14,000 ft (4,300 m). By volume, the two largest Cascade volcanoes are the broad shields of Medicine Lake Volcano and Newberry Volcano, which are about 145 mi³ (600 km³) and 108 mi³ (450 km³) respectively. Mount Garibaldi and Glacier Peak are the only two Cascade volcanoes that are made exclusively of dacite.

Over the last 37 million years, the Cascade Arc has been erupting a chain of volcanoes along the Pacific Northwest. Several of the volcanoes in the arc are frequently active. The volcanoes of the Cascade Arc share some general characteristics, but each has its own unique geological traits and history. Lassen Peak in California, which last erupted in 1917, is the southernmost historically active volcano in the arc, while Mount Meager in British Columbia, which erupted about 2,350 years ago, is generally considered the northernmost member of the arc. A few isolated volcanic centers northwest of Mount Meager such as the Silverthrone Caldera, which is a circular 20 km wide, deeply dissected caldera complex, may also be the product of Cascadia subduction because andesite, basaltic andesite, dacite and rhyolite can be found at these volcanoes and elsewhere along the subduction zone. At issue are the current plate configuration and rate of subduction but based on chemistry is for these volcanoes to be subduction related and are therefore part of the Cascade Volcanic Arc. The Cascade Volcanic Arc appears to be segmented; the central portion of the arc is the most active and the northern end least active.

Lavas representing the earliest stage in the development of the Cascade Volcanic Arc mostly crop out south of the North Cascades proper, where uplift of the Cascade Range has been less, and a thicker blanket of Cascade Arc volcanic rocks has been preserved. In the North Cascades, geologists have not yet identified with any certainty any volcanic rocks as old as 35 million years, but remnants of the ancient arc’s internal plumbing system persist in the form of plutons, which are the crystallized magma chambers that once fed the early Cascade volcanoes. The greatest mass of exposed Cascade Arc plumbing is the Chilliwack batholith, which makes up much of the northern part of North Cascades National Park and adjacent parts of British Columbia beyond. Individual plutons range in age from about 35 million years old to 2.5 million years old. The older rocks invaded by all this magma were affected by the heat. Around the plutons of the batholith, the older rocks recrystallized. This contact metamorphism produced a fine mesh of interlocking crystals in the old rocks, generally strengthening them and making them more resistant to erosion. Where the recrystallization was intense, the rocks took on a new appearance dark, dense and hard. Many rugged peaks in the North Cascades owe their prominence to this baking. The rocks holding up many such North Cascade giants, as Mount Shuksan, Mount Redoubt, Mount Challenger, and Mount Hozomeen, are all partly recrystallized by plutons of the nearby and underlying Chilliwack batholith.

The Pemberton Volcanic Belt is an eroded volcanic belt north of the Garibaldi Volcanic Belt, which appears to have formed during the Miocene before fracturing of the northern end of the Juan de Fuca Plate. The Silverthrone Caldera is the only volcano within the belt that appears related to seismic activity since 1975.

The Garibaldi Volcanic Belt is the northern extension of the Cascade Arc. Volcanoes within the volcanic belt are mostly stratovolcanoes along with the rest of the arc, but also include calderas, cinder cones, and small isolated lava masses. The eruption styles within the belt range from effusive to explosive, with compositions from basalt to rhyolite. Due to repeated continental and alpine glaciations, many of the volcanic deposits in the belt reflect complex interactions between magma composition, topography, and changing ice configurations. Four volcanoes within the belt appear related to seismic activity since 1975, including: Mount Meager, Mount Garibaldi and Mount Cayley.

Mount Meager is the most unstable volcanic massif in Canada. It has dumped clay and rock several meters deep into the Pemberton Valley at least three times during the past 7,300 years. Recent drilling into the Pemberton Valley bed encountered remnants of a debris flow that had travelled 50 kilometers from the volcano shortly before it last erupted 2350 years ago. About 1,000,000,000 m³ of rock and sand extended over the width of the valley. Two previous debris flows, about 4,450 and 7,300 years ago, sent debris at least 32 kilometers from the volcano. Recently, the volcano has created smaller landslides about every ten years, including one in 1975 that killed four geologists near Meager Creek. The possibility of Mount Meager covering stable sections of the Pemberton Valley in a debris flow is estimated at about one in 2400 years. There is no sign of volcanic activity with these events. However scientists warn the volcano could release another massive debris flow over populated areas anytime without warning.

In the past, Mount Rainier has had large debris avalanches, and has also produced enormous lahars due to the large amount of glacial ice present. Its lahars have reached all the way to the Puget Sound. Around 5,000 years ago, a large chunk of the volcano slid away and that debris avalanche helped to produce the massive Osceola Mudflow, which went all the way to the site of present-day Tacoma and south Seattle. This massive avalanche of rock and ice took out the top 1,600 feet (500 m) of Rainier, bringing its height down to around 14,100 feet (4,300 m). About 530 to 550 years ago, the Electron Mudflow occurred, although this was not as large-scale as the Osceola Mudflow.

While the Cascade volcanic arc (a geological term) includes volcanoes such as Mount Meager and Mount Garibaldi, which lie north of the Fraser River, the Cascade Range (a geographic term) is considered to have its northern boundary at the Fraser.

Cascadia subduction zone

The Cascade Volcanoes were formed by the subduction of the Juan de Fuca, Explorer and the Gorda Plate (remnants of the much larger Farallon Plate) under the North American Plate along the Cascadia subduction zone. This is a 680 mi (1,094 km) long fault, running 50 mi (80 km) off the west-coast of the Pacific Northwest from northern California to Vancouver Island, British Columbia. The plates move at a relative rate of over 0.4 inches (10 mm) per year at a somewhat oblique angle to the subduction zone.

Because of the very large fault area, the Cascadia subduction zone can produce very large earthquakes, magnitude 9.0 or greater, if rupture occurred over its whole area. When the “locked” zone stores up energy for an earthquake, the “transition” zone, although somewhat plastic, can rupture. Thermal and deformation studies indicate that the locked zone is fully locked for 60 kilometers (about 40 miles) downdip from the deformation front. Further downdip, there is a transition from fully locked to aseismic sliding.

Unlike most subduction zones worldwide, there is no oceanic trench present along the continental margin in Cascadia. Instead, terranes and the accretionary wedge have been uplifted to form a series of coast ranges and exotic mountains. A high rate of sedimentation from the outflow of the three major rivers (Fraser River, Columbia River, and Klamath River) which cross the Cascade Range contributes to further obscuring the presence of a trench. However, in common with most other subduction zones, the outer margin is slowly being compressed, similar to a giant spring. When the stored energy is suddenly released by slippage across the fault at irregular intervals, the Cascadia subduction zone can create very large earthquakes such as the magnitude 9 Cascadia earthquake of 1700.

The Caribbean Plate is a mostly oceanic tectonic plate underlying Central America and the Caribbean Sea off the north coast of South America.

Roughly 3.2 million square kilometers (1.2 million square miles) in area, the Caribbean

Plate borders the North American Plate, the South American Plate, the Nazca Plate and the Cocos Plate. These borders are regions of intense seismic activity, including frequent earthquakes, occasional tsunamis, and volcanic eruptions.

Boundary types

The northern boundary with the North American plate is a transform or strike-slip boundary which runs from the border area of Belize, Guatemala (Motagua Fault), and Honduras in Central America, eastward through the Cayman trough on south of the southeast coast of Cuba, and just north of Hispaniola, Puerto Rico, and the Virgin Islands. Part of the Puerto Rico Trench, the deepest part of the Atlantic Ocean (roughly 8,400 meters), lies along this border. The Puerto Rico trench is at a complex transition from the subduction boundary to the south and the transform boundary to the west.

The eastern boundary is a subduction zone, the Lesser Antilles subduction zone, where oceanic crust of the South American Plate is being subducted under the Caribbean Plate. Subduction forms the volcanic islands of the Lesser Antilles Volcanic Arc from the Virgin Islands in the north to the islands off the coast of Venezuela in the south. This boundary contains seventeen active volcanoes, most notably Soufriere Hills on Montserrat;, Mount Pelée on Martinique; La Grande Soufrière on Guadeloupe; Soufrière Saint Vincent on Saint Vincent; and the submarine volcano Kick-’em-Jenny which lies about 10 km north of Grenada. Large historical earthquakes in 1839 and 1843 in this region are possibly megathrust earthquakes.

Along the geologically complex southern boundary, the Caribbean Plate interacts with the South American Plate forming Barbados, Trinidad and Tobago (all on the Caribbean Plate), and islands off the coast of Venezuela (including the Leeward Antilles) and Colombia. This boundary is in part the result of transform faulting along with thrust faulting and some subduction. The rich Venezuelan petroleum fields possibly result from this complex plate interaction.

The western portion of the plate is occupied by Central America. The Cocos Plate in the Pacific Ocean is subducted beneath the Caribbean Plate, just off the western coast of Central America. This subduction forms the volcanoes of Guatemala, El Salvador, Nicaragua, and Costa Rica, also known as the Central America Volcanic Arc.

Origin

There are two contending theories as to the origin of the Caribbean Plate.

One holds that it is a large igneous province that formed in the Pacific Ocean tens of millions of years ago. As the Atlantic Ocean widened, North America and South America were pushed westward, separated for a time by oceanic crust. The Pacific Ocean floor subducted under this oceanic crust between the continents. The Caribbean Plate drifted into the same area, but as it was less dense (although thicker) than the surrounding oceanic crust, it did not subduct, but rather overrode the ocean floor, continuing to move eastward relative to North America and South America. With the formation of the Isthmus of Panama 3 million years ago, it ultimately lost its connection to the Pacific.

A more recent theory asserts that the Caribbean Plate came into being from an Atlantic hotspot which no longer exists. This theory points to evidence of the absolute motion of the Caribbean Plate which indicates that it moves westward, not east, and that its apparent eastward motion is only relative to the motions of the North American Plate and the South American Plate.

The Alpine Fault is a geological fault, specifically a right-lateral strike-slip fault, that runs almost the entire length of New Zealand’s South Island. It forms a transform boundary between the Pacific Plate and the Indo-Australian Plate. Earthquakes along the fault, and the associated earth movements, have formed the Southern Alps. The uplift to the southeast of the fault is due to an element of convergence between the plates, meaning that the fault has a significant high-angle reverse oblique component to its displacement.Transform Boundary – Alpine Fault, South Island, New Zealand The Alpine Fault is a geological fault, specifically a right-lateral strike-slip fault, that runs almost the entire length of New Zealand’s South Island. It forms a transform boundary between the Pacific Plate and the Indo-Australian Plate. Earthquakes along the fault, and the associated earth movements, have formed the Southern Alps. The uplift to the southeast of the fault is due to an element of convergence between the plates, meaning that the fault has a significant high-angle reverse oblique component to its displacement.

The Alpine Fault is believed to align with the Macquarie Fault Zone in the Puysegur Trench off the southwestern corner of the South Island. From there, the Alpine Fault runs along the western edge of the Southern Alps, before splitting into a set of smaller dextral strike-slip faults north of Arthur’s Pass, known as the Marlborough Fault System. This set of faults, which includes the Wairau Fault, the Hope Fault, the Awatere Fault, and the Clarence Fault, transfer displacement between the Alpine Fault and the Hikurangi subduction zone to the north. The Hope fault is thought to represent the primary continuation of the Alpine fault.

Tectonic setting of New Zealand: astride a plate boundary which includes the Alpine Fault

New Zealand lies at the edge of both the Australian and Pacific tectonic plates. To the northeast of New Zealand, and underneath North Island, the Pacific Plate is moving towards, and being subducted below the Australian Plate. To the south of New Zealand, and underneath Fiordland, the two plates are also moving toward each other but here the Australian Plate is being subducted under the Pacific Plate.

The Australian and Pacific Plates generally don’t move smoothly past each other. They move in a series in a small rapid motions each of which is accompanied by one or more earthquakes.

Deep earthquakes under North Island form a well defined band (seismic zone) running northeast from Marlborough through White Island. Shallow earthquakes tend to occur to the southeast of this seismic zone, while the deeper ones occur towards the northwest. The earthquakes form this pattern occur where the Pacific Plate is being subducted under the Australian Plate. This pattern of deeper earthquakes towards the northwest of North Island reflects the northwest dip (or slope) of the boundary between the two plates (the Benioff zone).

Conversely, in the southwest of South Island where the Australian Plate is being subducted below the Pacific Plate, the deeper earthquakes occur on the southeast edge of the seismic zone where the Benioff zone dips steeply to the southeast.

Volcanoes

As the Pacific Plate is subducted below North Island, the part of the Australian Plate that makes up the central North Island is stretched and has, over many millions of years, become thinner than normal crust. Water released from the Pacific Plate deep under North Island combines with the hot rock of the Australian Plate at about 100km depth and causes a small amount of that rock to melt. This molten rock rises to the surface through the thinned crust and is either erupted from volcanoes like Ruapehu, Tongariro and Ngaruhoe or sits within the crust and heats it, and the water it contains, up causing geothermal activity around Taupo and Rotorua. The area of volcanic activity is referred to as the Taupo Volcanic Zone (see map above).

South Island Faults

The subduction zone in the north is linked to the subduction zone in the south by a series of very large faults that run through Marlborough (Marlborough Fault System) and down the west coast of South Island (Alpine Fault). The Marlborough Fault System is a series of subparallel strike-slip faults which run northeast-southwest. Relative movement across the Marlborough Fault System is dextral or right-lateral.

Note : The above story is reprinted from materials provided by Wikipedia & Department of Geology, University of Otago, New Zealand
Plate Boundary By : USGS 

The Kuril islands, extending from north to south for 1200 km, are a part of the submarine

uplift located between the Sea of Okhotsk basin and the Kuril oceanic trench*. The archipelago comprises 30 large islands and numerous small ones. Two sectors, different in the history of development and morphology are distinguished within the archipelago (Luchitsky, 1974; Piskunov, 1987). The inner arc, known as the Greater Kuril,

extends from Shumshu island to Kunashir and the outer arc, termed the Lesser Kuril, which includes Shikotan and the small isles of the Habomai group (Figure1).

Tectonics and Environmental Change

Tectonically the Kurils belong to the Kuril-Kamchatka island arc which is related, as all island arcs, to an oceanic trench located 150-170 km from the volcanic front. Pronounced seismic activity is associated with the arc and the Benioff zone can be traced to a depth of 650 km (Tarakanov, 1972). The Greater Kurils and the Lesser Kurils differ in their morphology, geological structure, and history of development.

The Lesser Kurils, as well as the submarine Vityaz uplift to which they are connected and the peninsulas of eastern Kamchatka, are interpreted as an outer non-volcanic arc of the Kuril-Kamchatka system. The Lesser Kurils are formed mainly by late Cretaceous volcanic rocks. Volcanism of a submarine nature, as a result of which the islands emerged, was active in the Campanian (85-80 Ma BP) and the geological complex of this age is represented mainly by basalts. In the Maastrichtian (73-65 Ma BP), volcanic activity faded and flysh with olistostromes accumulated. Volcanic activity of the time was represented mainly by magmatic intrusions into sediments (Piskunov and Sergeev, 1992). At the end of the Cretaceous, volcanism occurred in terrestrial conditions. The completion of the magmatic activity was marked by gabbro intrusions. At present, there are no active volcanoes in the Lesser Kurils. The ancient calderas have been eroded and gentle hills with a height of 150-250 m dominate the islands.

The Greater Kurils are a younger formation where volcanism commenced at about 30 Ma BP in the late Oligocene-early Miocene. There were three major stages of arc development and these are reflected in the sequence of Cenozoic rocks (Fedorchenko et al., 1989; Piskunov and Sergeev, 1992). The most ancient rocks of the lower Miocene age comprise basalts, andesites, rhyolites, and their tuffs. The latter are abundant and can be correlated with the Green Tuff Formation of Japan. During the next stage in the middle Miocene, volcanism occurred mainly under terrestrial conditions and the stratigraphy is characterized by the occurrence of both volcanic rocks and flysh-type sequences.

Clastic material contains rocks which are not found in the Greater Kurils and which have apparently been derived from the dissected terrain in the back-arc area. The composition of these sequences shows that the Sea of Okhotsk basin did not exist at the time, while their inclined position reflects block rotation along faults during rifting and the opening of the Sea of Okhotsk basin at about 15 Ma BP (Zonenshain et al., 1990). The latest stage, during which the modern volcanic cones emerged, began in the late Miocene and is continuing at present. Its geology is a typical cal-calkaline volcanic sequence.

Similarly to Kamchatka, there were major periods of enhanced volcanic activity in the Kurils in the late Pleistocene and early Holocene (e.g., the Medeleev and Golovnin calderas formed 38-40 Ka BP). Over a hundred terrestrial volcanoes occur on the islands at present and 39 of them are active. The most active volcanoes are the tallest Kuril volcano, the Alaid (2339 m) located in the north of the arc and the Sarychev located on Matua island. The last powerful eruption of the Alaid occurred in 1972 when a new slag cone 150 m high formed in the centre of the volcano. The Sarychev is known for its regular activity. The most violent eruptions occurred in 1930 and 1946 when the ashfalls reached central Kamchatka. By contrast, another major volcano, the Golovnin caldera (the southernmost Kuril volcano located in Kunashir island) has not erupted for more than a century although it accommodates geothermal springs and two large lakes formed 640-680 years BP (Razjigaeva et al., 1998).

Typical of the Kurils is low to middle mountainous relief with altitudes of 500-1300 m. Five major morphological types of relief are distinguished: volcanic, seismo-tectonic, erosive-denudational, coastal (of abrasion and accumulation types), and aeolian (Grabkov and Isachenko, 1982). Aeolian forms date back to about 4.5-4.7 Ka BP when an extensive marine regression occurred (Bazarova et al., 1998). Most islands have volcanic relief and the landscape is that of individual volcanoes or volcanic ridges linked by sediment-filled isthmuses. Six to seven marine terraces occur in the coastal zone with altitudes ranging between 2-3 and 200-250 m a.s.l. Both marine terraces and volcanic massifs are strongly dissected which indicates a high rate of erosion and marine abrasion.

The landscapes of the Kuril islands were formed under the influence of two major factors: volcanism and seismic activity, and climate change. Climate is strongly influenced by the physical and chemical properties of the ocean, such as sea surface temperature and salinity, and variability in the paths of the oceanic currents may result in regional climatic change. Periodic changes in ocean circulation patterns due to changes in trade wind intensity in the eastern equatorial North Pacific Ocean and movements of the ocean plate have been discussed in relation to the warm Kuroshio current and climate change in Japan (Taira, 1980; Sawada and Handa, 1998). The islands of Japan and the Kurils are located in close proximity (as early as in the middle Holocene the islands of Hokkaido and Kunashir were connected by a landbridge) and climatic and environmental changes in northern Japan and the southern Kurils are closely correlated (Bazarova et al., 1998). However, the paleooceanography of the Kurils and its impact on the landscape development require further independent investigation.

*Kuril–Kamchatka Trench