Academic Reading — Test 111

Reading passage

Iceland occupies an unusual position on the surface of the planet. The island sits astride the Mid-Atlantic Ridge, the long undersea boundary where the North American and Eurasian tectonic plates are gradually pulling apart. As these plates separate by roughly two centimetres each year, molten rock from deep within the Earth rises to fill the widening gap, creating a series of volcanic rift zones that run diagonally across the country. This geological setting brings extraordinary heat close to the surface, and it is this heat, rather than the island's modest reserves of fossil fuel, that has shaped the nation's approach to energy. Few other inhabited places offer such convenient access to the warmth stored within the crust. The fundamental principle behind geothermal power is straightforward. Rainwater and melted snow seep down through fractured rock until they reach regions heated by the underlying magma. There the water may reach temperatures well above the ordinary boiling point, remaining liquid only because it is held under great pressure. Engineers drill boreholes, sometimes more than two kilometres deep, to reach these reservoirs of superheated water and steam. When the hot fluid travels up the borehole and the pressure drops, much of it flashes instantly into steam. This steam is then directed through turbines, whose spinning blades drive generators that produce electricity. The water that remains after this process is far from useless; it still carries substantial warmth and is frequently channelled into a second, lower-temperature stage of generation or passed directly into heating networks. Iceland exploits its underground heat in two broad ways, and the distinction matters. High-temperature fields, which lie within or very near the active rift zones, are reserved chiefly for generating electricity, since only there is the heat intense enough to drive turbines efficiently. Low-temperature fields, found further from the volcanic centres, supply warm water for a quite different purpose. In the capital, Reykjavik, and in most other towns, hot water is pumped from the ground and circulated through insulated pipes to warm homes, schools and offices. This arrangement, known as district heating, means that the overwhelming majority of Icelandic buildings are heated without burning any fuel at all. The same warm water also supplies the open-air swimming pools that are a feature of almost every community, and is used to heat greenhouses in which vegetables and even bananas are grown despite the harsh climate outside. The advantages of this resource are considerable, yet it would be misleading to present it as entirely without difficulty. Because the heat originates within the Earth and is continually replenished, geothermal energy is usually classed as renewable, and it produces far less carbon dioxide than coal or gas. However, the underground water is not pure. It often contains dissolved minerals and gases, including hydrogen sulphide, which gives some geothermal areas a faint smell of rotten eggs and which must be carefully managed. The fluid is also corrosive, gradually damaging pipes and equipment that therefore require regular maintenance and replacement. A further concern is that a reservoir can be drawn upon faster than nature refills it; if too much water is extracted, the pressure and temperature of a field may fall over time, reducing its output. For this reason, operators increasingly pump spent water back underground, a practice that helps to sustain the reservoir and reduces waste at the surface. One of the most striking examples of how these processes are linked is the Blue Lagoon, a large pool of warm, mineral-rich water in a lava field on the Reykjanes peninsula. Although it is now a celebrated attraction visited by travellers from around the world, the lagoon was never planned as such. It formed accidentally from water discharged by a neighbouring power station, and only later did people discover that bathing in it appeared to soothe certain skin conditions. The site is a reminder that geothermal development can yield benefits that were never originally intended. Looking ahead, Icelandic engineers have begun to investigate whether even greater quantities of energy might be obtained by drilling deeper, towards rock that is hotter still. Experimental wells have reached layers where the conditions are so extreme that the fluid exists in an unusual state, neither simply liquid nor ordinary steam. A single such well, in theory, could yield several times the power of a conventional one, though the engineering challenges are formidable and the technology remains unproven on a large scale. Whether or not these deep wells eventually succeed, Iceland already stands as a clear demonstration that a country positioned over a volcanic rift can turn the restless geology beneath its feet into a steady and largely clean supply of energy.