Historic Entrance (Mammoth Cave, Kentucky, USA) 51 : 無料・フリー素材/写真
Historic Entrance (Mammoth Cave, Kentucky, USA) 51 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | (photo by Ljubomir Risteski)--------------------------------------Western Kentucky’s Mammoth Cave is the longest known cave on Earth, with over 426 miles of mapped passages as of fall 2022. In a good year, 5 to 6 miles worth of new Mammoth Cave passages are found and mapped. Cave mapping shows that Mammoth Cave passages are about 700 feet away from caves at Fisher Ridge, where 130 miles worth of passages are known. Mammoth Cave’s total known length will jump to over 550 miles if a connection is made (both sides have “agreed” to not look for a connection - it's a sad, anti-science stance, due to politics). It’s been estimated that Mammoth Cave may consist of 600 to 1000 miles of passages. Casual visitors can see about 12 miles worth of Mammoth Cave’s passages on various tours. The name “Mammoth Cave” refers to the immense size of many of the rooms and passages. The name does not refer to its world-record length, nor to the early discovery of mammoth fossils here (actually, fossil proboscidean skeletal remains have been reported from this locality). The cave is developed in Middle and Upper Mississippian limestones. Partial dissolution of these limestones started during the late Cenozoic, since at least the Pliocene (the last ~5 million years). Limestone dissolution results from the presence of slightly acidic groundwater. Groundwater originates as rain, snowmelt, or runoff. It percolates through joints and bedding planes of the limestones and slowly dissolves them. Why is the groundwater slightly acidic? Rainwater is slightly acidic due to the presence of carbonic acid (H2CO3), the result of water-atmosphere interactions (H2O plus CO2 yields H2CO3). Once in the ground, water becomes more acidic by picking up complex organic acids from soils and additional carbonic acid. Air occupying spaces in soil is enriched in carbon dioxide gas, so groundwater will end up having more carbonic acid than it did as rain.Groundwater dissolution has produced a vast network of passages in Mammoth Cave that vary in height, width, and cross-section shape. Passage types include tubular passages, canyon passages, giant canyon passages, keyhole passages, and domepits (vertical shafts).The elevation of the water table in the Mammoth Cave area has been dropping over the past 5 million years. Currently, the water table in the cave is almost at the same level as the Green River, the main drainage in the area. So, the lowest passages of Mammoth Cave are partially to fully flooded. All the passages above that are dry to mostly dry. The upper dry levels indicate where the water table used to be. Depending on how one counts “levels”, Mammoth Cave has 6 or 7 levels. They are traditionally named Levels A (top) to F (bottom). Recently, Mammoth Cave levels have been redesignated A to D.Seen here is Mammoth Cave's Historic Entrance. Many of the currently-offered cave tours enter here. The rocks at the mouth of the cave are part of the Beaver Bend Member of the Girkin Limestone (lower Chesterian Series, lower Upper Mississippian). Reported lithologies in the Beaver Bend include lime mudstones (micrites; micritic limestones), some fossiliferous to oolitic wackestones, and lime mudstones having patches of coarsely-crystalline calcite spar (dismicrite).It is not certain exactly when Mammoth Cave was discovered. A story about its 1797 discovery by a man named Houchins (or Hutchins) is fictional (the park service knows this, but still tells the story during cave tours). However, Mammoth Cave’s earliest acknowledgement in available historical records dates to 1797.The entrance waterfall is often a heavy trickle; it becomes more energetic after rain events. Water emerges from a spring above the upper rim of the mouth of the cave, drops into a rubble-filled domepit. The water re-emerges at River Styx Spring, where it drains into the Green River. |
| 撮影日 | 2019-03-10 09:34:17 |
| 撮影者 | James St. John |
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