Caves Reading Passage
Caves Reading Passage
Paragraph A: Man can enter natural underground spaces, commonly called caves. They are differentiated into three types: highly widespread and extensive are the ones in soluble rocks, and they are usually limestone or marble are formed by underground water; cliffs are formed on the coast and are generally concentrated pounding of waves along joints and zones of crushed rock; in the lava flows few caves are formed, where the solidified outer crust is left after the molten core has drained away to form rough tunnels, such as those on the small basalt volcanoes of Auckland.
Paragraph B: Many regions of New Zealand feature limestone formations, but not all of them are cavernous formations, spanning geological epochs from the most recent to more than 450 million years ago. Although many caverns have been found, there are still hundreds that have yet to be investigated. The Te Kuiti Group (Oligocene) rocks from Port Waikato south to Mokau and from the coast inland to the Waipa Valley - especially in the Waitomo district - are the most notable limestone areas for caves, covering hundreds of square kilometres, and the Mount Arthur Marble (Upper Ordovician) of the mountains of northwest Nelson are the most notable areas for caves, covering tens of square kilometres (fringed by thin bands of Oligocene limestone in the valleys and near the coast).
Paragraph C: The thickness of horizontal rocks or beds is 5-7.5 cm of sedimentary rocks (including limestone). An estimated thickness of one hundred metres. Cracks along the partings and joints at angles to them form in pure limestone because of folding caused by earth movements. The water table is the level at which all fractures and pores in the earth and the underlying rocks are filled with water, having percolated down through the soil and the cracks in the rocks. By dissolving the limestone along the joints, this acidic water creates a tunnel, which is further widened by the abrasive action of sand and pebbles brought by streams. The widespread solution occurs between the seasonal boundaries of the water table. Both continued erosion and the deposition of floor or silt and pebbles can alter stream patterns. The water flow that originally carved out most caverns is still present.
Paragraph D: Many of the caves in the Oligocene limestones, which are softer and have more uniform bedding, have developed horizontally, with multiple levels and corridors that can be rather lengthy. Gardner's Gut in Waitomo consists of around seven kilometres of tunnels spread across two main levels. Plan views of caves often highlight notable features such as long, narrow, straight tunnels that follow joint patterns like in Ruakuri and Waitomo or a series of parallel straits orientated in one or more directions like in Te Anaroa and Rockville. Burr Cave in Waitomo has a tall and narrow vertical cross-section because it follows joints, while Hollow Hill in Waitomo is 233 metres long, 59.4 metres wide, and 30.48 metres high; Luckie Strike in Waitomo is low and wide because it follows bedding planes; and Rangitaawa Shaft in Waitomo is a high vertical water-worn shaft (91 m). Many of the Waitomo Caves reach depths of several hundred metres, with the deepest being Harwood Hole, located in the town of Takaka. These caves are found in the tougher, massive Mount Arthur Marble (a metamorphosed limestone) (370m).
Paragraph E: Mineral encrustations, which can cover a cave's roof, floor, and walls, give caves distinctive beauty. Stalactites, from the Greek stalagmites, meaning "dripping," are crystalline calcium carbonate (calcite) growths that precipitate from groundwater seepage. They typically range in colour from white to yellow but can also be brown or even crimson. A long, thin straw that may reach the floor or thicken into columns forms in areas where water evaporates more quickly than it pours. A thin curtain, resembling a stage curtain, can be created if the water source is moved across the ceiling. The term "helictite" is used to describe a type of stalactite that branches or curls. Conical or gnarled floor growths called stalagmites (Greek for "that which dripped") occur when water drips faster than it evaporates and causes splashing. Massive columns may arise from these if they were allowed to grow upwards. It is possible for pools of water to build up their edges to form narrow walls of brimstone in areas where calcite is deposited by water spreading thinly over the walls or floor. White gypsum (calcium sulphate) crystal habits in cave deposits are likely related to relative humidity. The gypsum flower is the most stunning variety; it grows from a single point on the cave wall and spreads its petals outward and upward like a lily or orchid.
Caves Reading Questions and Answers
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