Physical Environments Earth Systems

1. Physical Environments Earth Systems

2. 1.1.2 Variations in the characteristics and locations of igneous activity

3. You need to know the pattern of distribution of volcanic activity in elation to plate boundaries and in anomalous locations such as hot-spots. You need to be able to describe and explain the characteristics and formation of lava plateaux and different volcanic cones (acid, basic, composite, caldera and fissure)

4. Caldera The largest and most explosive volcanic eruptions eject tens to hundreds of cubic kilometres of magma onto the Earth's surface. When such a large volume of magma is removed from beneath a volcano, the ground subsides or collapses into the emptied space, to form a huge depression called a caldera. Some calderas are more than 25 km in diameter and several kilometres deep. Part of Crater Lake caldera, Oregon, U.S.A. Diameter about 8 kilometres. View is toward the east and includes a late-stage volcano in crater named Wizard Island.

5. Cinder Cones and Scoria ConesCinder cones are the simplest type of volcano. They are built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than 300m or so above their surroundings. Cinder cones are numerous in western North America as well as throughout other volcanic terrains of the world. -- Cinder cone at Little Lake, California.

6. Composite Volcanoes (Stratovolcanoes). Some of the Earth's grandest mountains are composite volcanoes. They are typically steep-sided, symmetrical cones of large dimension built of alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs and may rise as much as 2000m above their bases. Some of the most conspicuous and beautiful mountains in the world are composite volcanoes, including Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mount Shasta in California, Mount Hood in Oregon, Mount St. Helens and Mount Rainier in Washington. Most composite volcanoes have a crater at the summit which contains a central vent or a clustered group of vents. Lavas either flow through breaks in the crater wall or issue from fissures on the flanks of the cone. Lava, solidified within the fissures, forms dykes that act as ribs which greatly strengthen the cone.

7. The essential feature of a composite volcano is a conduit system through which magma from a reservoir deep in the Earth's crust rises to the surface. The volcano is built up by the accumulation of material erupted through the conduit and increases in size as lava, cinders, ash, etc., are added to its slopes. St. Augustine volcano, Alaska

8. Acid Lava Cones: In the typical "continental" environment, volcanoes are located in unstable, mountainous belts that have thick roots of granite or andesitic rock. Magmas, generated near the base of the mountain root, rise slowly or intermittently along fractures in the crust. During passage through the continental crust, magmas are commonly modified or changed in composition and erupt on the surface to form volcanoes constructed of andesitic rocks. The volcanoes of island arcs are usually andesitic In a typical "island-arc" environment, volcanoes lie along the crest of an arcuate, crustal ridge bounded on its convex side by a deep oceanic trench. The granite or granite like layer of the continental crust extends beneath the ridge to the vicinity of the trench. Basaltic magmas, generated in the mantle beneath the ridge, rise along fractures through the granitic layer. These magmas commonly will be modified or changed in composition during passage through the granitic layer and erupt on the surface to form volcanoes built largely of andesitic rocks.

9. Lava Domes Lava (usually dacite or rhyolite) that is too (viscous) sticky to flow far from its vent forms steep-sided mounds called lava domes. Mount Unzen and Shimabara City, Kyushu, Japan.

10. Lava Plateaus In some shield-volcano eruptions, basaltic lava pours out quietly from long fissures instead of central vents and floods the surrounding countryside with lava flow upon lava flow, forming broad plateaus. Lava plateaus of this type can be seen in Iceland, south-eastern Washington, eastern Oregon, and southern Idaho. Lava Beds National Park. Tulelake, California

11. Basic Lava Cones In a typical "oceanic" environment, volcanoes are aligned along the crest of a broad ridge that marks an active fracture system in the oceanic crust. Basaltic magmas, generated in the upper mantle beneath the ridge, rise along fractures through the basaltic layer. Because the granitic crustal layer is absent, the magmas are not appreciably modified or changed in composition and they erupt on the surface to form basaltic volcanoes. Shield Volcanoes Shield volcanoes are built almost entirely of fluid lava flows. Flow after flow pours out in all directions from a central summit vent, or group of vents, building a broad, gently sloping cone of flat, domical shape, with a profile much like that a a warrior's shield. They are built up slowly by the accretion of thousands of flows of highly fluid basaltic (from basalt, a hard, dense dark volcanic rock) lava that spread widely over great distances, and then cool as thin, gently dipping sheets. Lavas also commonly erupt from vents along fractures (rift zones) that develop on the flanks of the cone. Some of the largest volcanoes in the world are shield volcanoes.

12. In northern California and Oregon, many shield volcanoes have diameters of 3 or 4 miles and heights of 1,500 to 2,000 feet. The Hawaiian Islands are composed of linear chains of these volcanoes including Kilauea and Mauna Loa on the island of Hawaii -- two of the world's most active volcanoes. The floor of the ocean is more than 15,000 feet deep at the bases of the islands. As Mauna Loa, the largest of the shield volcanoes (and also the world's largest active volcano), projects 13,677 feet above sea level, its top is over 28,000 feet above the deep ocean floor.

13. Submarine Volcanoes, Ridges, and VentsSubmarine volcanoes and volcanic vents are common features on certain zones of the ocean floor. Some are active at the present time and, in shallow water, disclose their presence by blasting steam and rock-debris high above the surface of the sea. Many others lie at such great depths that the tremendous weight of the water above them results in high, confining pressure and prevents the formation and explosive release of steam and gases. Even very large, deepwater eruptions may not disturb the ocean surface. Tuyas:A volcano formed under a glacier. Because volcanic activity in western Canada was contemporaneous with the ebb and flow of Cordilleran glaciations, many of the volcanoes display ice contact features. Mount Garibaldi itself is a supraglacial volcano which erupted onto a regional ice sheet. Others, such as Hoodoo Mountain, were contained within basins thawed in the ice and assumed the flat-topped form of tuyas. Still others, such as the subglacial mounds of the Clearwater Field, were erupted under glacial ice to form piles of pillow lava and hyaloclastite.

14. Igneous intrusions are bodies of igneous rock which form due to the crystallization of magma underground. Igneous intrusions are also referred to as plutons. There are a number of different types of intrusions. These are classified based on their sizes and shapes. View from the summit of West Spanish Peak of Goemmer Butte and Profile Dike in Colorado. A variety of intrusive features dominate the landscape.

15. Dykes are small, tabular intrusive rock bodies. They form as magma, forced into fractures of rock already present in an area (called country rock), cools and crystallizes. Dykes are considered to be discordant intrusive bodies because they cut across pre-existing rocks. A composite basalt dyke.  One of many in the Tertiary dyke swarm at Kildonan on the Islec of Arran

16. Sills form within Earth's crust as magma intrudes in between layers of rock and then crystallizes. Sills, therefore, are concordant intrusive rock. Like dykes, sills are tabular or sheet like in their shapes. Clauchland's Sill The composite sill at Drumadoon Point on Arran

17. Views of the Whin Sill with Scale Force and Hadrian's Wall in Northumbria

18. Volcanic plugs or necks are relatively uncommon igneous intrusions. They form when magma crystallizes within the neck of a volcano, and are exposed for us to see as weathering and erosion remove the rock comprising the volcano. Ailsa Craig of the Isle of Arran is a example of a volcanic plug or volcanic neck.

19. Colorado: East Spanish Peak, which intruded after West Spanish Peak, is on the left; West Spanish Peak is on the right. The dark rock in front of the Spanish Peaks is Goemmer Butte (pronounced "Gimmer"), a volcanic plug that intruded into the Cuchara Formation as part of the Spanish Peak intrusives

20. Batholiths are the largest of all igneous intrusions. They are formed by the massive invasion of hot magma into country rock. Such a large intrusion can melt or metamorphose most rocks. Cooling of the magma can take thousands of years. Like dykes, batholiths cut through pre-existing rocks, so they are discordant intrusions. Many of the rocks exposed the surface in California are granite batholiths. Batholiths have been interpreted as a late stage in the development of mountain chains associated with continent collision.

21. The Dartmoor granite is the largest of six granite regions and three smaller outcrops, which form the spine of the Southwest peninsula. It is the surface expression of a much larger mass hidden underground by the surrounding rocks. Although the granites of the south west vary in chemistry, crystal size and in the ages given to them by radiometric dating techniques, they are thought to be part of a much larger granitic mass underlying the region. • Isles of Scilly • Land’s End • St Austell • Red Ruth Moor • Bodmin Moor • Dartmoor

22. You need to know a range of economic benefits (i.e. leading to employment and spending in the local community) of igneous activity. You should be able to refer to the economic benefits of the located landscapes that you have studied already, such as the Andes, Iceland or Dartmoor.

23. THE ECONOMIC BENEFITS OF IGNEOUS ACTIVITY There are certain economic and social benefits to be gained from living in areas of tectonic activity. When students are asked to consider their benefits, they invariably start by saying that 'houses must be cheap because no-one wants to live there..', but clearly people do: over a million people live on the slopes of Mount Vesuvius alone, and others return to their homes on the slopes of Mt. Merapi on Java despite the dangers. BUILDING MATERIALS Naturally broken aggregate: cinder tracks for athletics; building stone such as granite which is extensive used in building because of its strength and attractive appearance. Dundee is sometimes referred to as Granite City.

24. MINERALS People have mined gems and metals. Diamonds and opals are found in volcanic vents. Most of the metallic minerals mined in the world, such as copper, gold, silver, lead, and zinc, are associated with magmas found deep within the roots of extinct volcanoes located above subduction zones. Rising magma does not always reach the surface to erupt; instead it may slowly cool and harden beneath the volcano to form a wide variety of crystalline rocks (generally called plutonic or granitic rocks). Some of the best examples of such deep-seated granitic rocks, later exposed by erosion, are magnificently displayed in California's Yosemite National Park. Ore deposits commonly form around the magma bodies that feed volcanoes because there is a ready supply of heat, which convectively moves and circulates ore-bearing fluids. The metals, originally scattered in trace amounts in magma or surrounding solid rocks, become concentrated by circulating hot fluids and can be redeposited, under favourable temperature and pressure conditions, to form rich mineral veins.

25. The active volcanic vents along the spreading mid-ocean ridges create ideal environments for the circulation of fluids rich in minerals and for ore deposition. Water as hot as 380 °C gushes out of geothermal springs along the spreading centres. The water has been heated during circulation by contact with the hot volcanic rocks forming the ridge. Deep-sea hot springs containing an abundance of dark-coloured ore minerals (sulphides) of iron, copper, zinc, nickel, and other metals are called "black smokers." On rare occasions, such deep-sea ore deposits are later exposed in remnants of ancient oceanic crust that have been scraped off and left ("beached") on top of continental crust during past subduction processes. The Troodos Massif on the Island of Cyprus is perhaps the best known example of such ancient oceanic crust. Cyprus was an important source of copper in the ancient world, and Romans called copper the "Cyprian metal"; the Latin word for copper is cyprium.

26. GEOTHERMAL ENERGY Geothermal energy can be harnessed from the Earth's natural heat associated with active volcanoes or geologically young inactive volcanoes still giving off heat at depth. Steam from high-temperature geothermal fluids can be used to drive turbines and generate electrical power, while lower temperature fluids provide hot water for space-heating purposes, heat for greenhouses and industrial uses, and hot or warm springs at resort spas. For example, geothermal heat warms more than 70 percent of the homes in Iceland, and The Geysers geothermal field in Northern California produces enough electricity to meet the power demands of San Francisco. In addition to being an energy resource, some geo-thermal waters also contain sulphur, gold, silver, and mercury that can be recovered as a by-product of energy production. In Reykjavik, Iceland, there are municipal pools which are heated by geothermal sources. The famous Blue Lagoon waters are around an hour's drive from the city. A free 24-hour geothermally heated pool is located at Nautholsvik beach, a mile from the city.

27. SOILS / FARMING People are prepared to take a gamble with a volcano when there is food to be grown. In Indonesia, the fertile soils of Mt. Merapi allow up to 3 crops a year to be grown and harvested. When volcanic ash weathers it releases minerals into the soil. Over thousands to millions of years, the physical breakdown and chemical weathering of volcanic rocks have formed some of the most fertile soils on Earth. In tropical, rainy regions, such as the windward (north-eastern) side of the Island of Hawaii, the formation of fertile soil and growth of lush vegetation following an eruption can be as fast as a few hundred years. Some of the earliest civilizations (for example, Greek, Etruscan, and Roman) settled on the rich, fertile volcanic soils in the Mediterranean-Aegean region. Some of the best rice-growing regions of Indonesia are in the shadow of active volcanoes. On the island of Lanzarote, the ground is so hot in places that hay left to dry can burst into flames. Farmers spread a 2 inch layer of black lava chips on their fields. These catch the morning dew and fogs and trap the moisture: a mulch. The moisture retention makes them particularly useful for viticulture and coffee.

28. RECREATION Hydrothermal activity: hot springs, geysers are associated with areas where the crust is thin, for example at Beppu in Japan. (see also earlier notes on Iceland) Hiking - popular tourist trips up Mt. Kilimanjaro, Mt. St. Helens, Yellowstone National Park. Crater Lake National Park in USA. MISCELLANEOUS INDUSTRIAL ITEMS Pumice stones - found in bathrooms for removing hard skin, or in facial pads. Cat litter - absorbent minerals. Stone used to 'stone-wash' jeans, as it is abrasive. Sulphur is mined from fumaroles. This is a poorly paid occupation in Indonesia. Volcanic glass shards are used in polishing compounds and as an abrasive in toothpaste and kitchen cleaners for surfaces.

29. Farmer ploughing a lush rice paddy in central Java, Indonesia. The Sundoro Volcano looms in the background. The most highly prized rice-growing areas have fertile soils formed from the breakdown of young volcanic deposits. (Photograph by Robert I. Tilling, USGS.)

30. RECREATION Hydrothermal activity: hot springs, geysers are associated with areas where the crust is thin, for example at Beppu in Japan. (see also earlier notes on Iceland) Hiking - popular tourist trips up Mt. Kilimanjaro, Mt. St. Helens, Yellowstone National Park. Crater Lake National Park in USA. MISCELLANEOUS INDUSTRIAL ITEMS Pumice stones - found in bathrooms for removing hard skin, or in facial pads. Cat litter - absorbent minerals. Stone used to 'stone-wash' jeans, as it is abrasive. Sulphur is mined from fumaroles. This is a poorly paid occupation in Indonesia. Volcanic glass shards are used in polishing compounds and as an abrasive in toothpaste and kitchen cleaners for surfaces.