1. Caves are natural underground spaces commonly those into which man can enter. There are three major types: the most widespread and extensive are those developed in soluble rocks, usually limestone or marble, by underground movement of water; on the coast are those formed in cliffs generally by the concentrated pounding of waves along joints and zones of crushed rock
Choose ONE WORD ONLY from the passage for each answer.
There are several 1……………. of caves with the most common and largest being located in limestone or marble. Coastal caves are created in cliffs usually by waves.
and a few caves are formed in lava flows, where the solidified outer crust is left after the molten core has drained away to form rough tunnels, like those on the small basalt volcanoes of Auckland.
. In lava flows, the solidified outer crusts that remain once the molten core has drained away also form 2…………………Limestone is to be found all over New Zealand, but not all of it contains caves.
2. Limestone of all ages, ranging from geologically recent times to more than 450 million years ago, is found in many parts of New Zealand, although it is not all cavernous. Many caves have been discovered, but hundreds still remain to be explored. The most notable limestone areas for caves are the many hundreds of square kilometres of 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; and the Mount Arthur Marble (Upper Ordovician) of the mountains of northwest Nelson (fringed by thin bands of Oligocene limestone in the valleys and near the coast).
While many caves are known, there are large numbers that have yet to be uncovered. The main 3…………………for limestone caves are Te Kuiti Group rocks
3. Sedimentary rocks (including limestone) are usually laid down in almost horizontal layers or beds which may be of any thickness, but most commonly of 5-7.5 cm. These beds may accumulate to a total thickness of about a hundred meters. Pure limestone is brittle, and folding due to earth movements causes cracks along the partings, and joints at angles to them. Rainwater percolates down through the soil and the fractures in the underlying rocks to the water table, below which all cavities and pores are filled with water. This water, which is usually acidic, dissolves the limestone along the joints and, once a passage is opened, it is enlarged by the abrasive action of sand and pebbles carried by streams. The extensive solution takes place between the seasonal limits of the water table. Erosion may continue to cut down into the floor, or silt and pebbles may build up floors and divert stream courses. Most caves still carry the stream that formed them.
Choose ONE WORD ONLY from the passage for each answer.
The Creation of Limestone Caves
limestone forms thick layers
earth moves creating 4………………………….at partings
rainwater trickling down through the soil and 5…………… in rocks
to the water table acidic water
dissolves limestone along joints
once 6…………………………. opened
extended by sand/pebbles taken along by 7………………8……………or silt and pebble accumulation changes stream course