An airport has two runways, one is North-South (N-S), and the other is East-West
ID: 1824019 • Letter: A
Question
An airport has two runways, one is North-South (N-S), and the other is East-West (E-W). Because of the prevailing winds, the E-W runway is used 80% of the days, and the N-S the remainder of the time. The selection of the runway for a given day is based on wind at the beginning of the day, and once selected will not be changed for the entire day. The airport has a single peak period each day; this is the hour between 4:00 and 5:00pm. During this peak hour, the volume of air traffic varies day to day and may be described with the normal variate N(100,10). The N-S runway is considered overcrowded of more than 125 planes use it during this period, whereas the E-W runway is considered overcrowded if more than 100 planes use it during a peak period.a. What is the probability that the N-S runway is going to be overcrowded on a given day, if at the beginning of the day the runway is selected to be used?
b. What would be the probability of overcrowding, if at the beginning of a given day the E-W runway were selected to be used?
c. What is the probability of overcrowding at the airport, if there is no advance information as to which runway will be used on a given day?
Explanation / Answer
Eldfell is a composite volcanic cone just over 200 metres (660 ft) high on the Icelandic island of Heimaey. It formed in a volcanic eruption which began without warning just outside the town of Heimaey on 23 January 1973. Its name means Mountain of Fire in Icelandic. The eruption caused a major crisis for the island and nearly led to its permanent evacuation. Volcanic ash fell over most of the island, destroying around 400 homes, and a lava flow threatened to close off the harbour, the island's main income source via its fishing fleet. An operation was mounted to cool the advancing lava flow by pumping sea water onto it, which was successful in preventing the loss of the harbour. After the eruption finished, the islanders used heat from the slowly cooling lava flows to provide hot water and to generate electricity. They also used some of the extensive tephra, fall-out of airborne volcanic material, to extend the runway at the island's small airport, and as landfill, on which 200 new houses were built. Contents [hide] 1 Background 2 The eruption begins 3 Evacuation 4 Destruction of houses, creation of land 5 Lava-cooling operations 6 The eruption dies down 7 Heimaey since the eruption 8 See also 9 References 10 Further reading 11 External links [edit]Background Iceland is a region of frequent volcanic activity, due to its location astride the Mid-Atlantic Ridge, where the North American and Eurasian Plates are moving apart, and also over the Iceland hotspot, which greatly enhances the volcanic activity. It is estimated that a third of all the basaltic lava erupted in the world in recorded history has been produced by Icelandic eruptions. The Vestmannaeyjar (Icelandic for Westman islands) archipelago lies off the south coast of Iceland, and consists of several small islands, all formed by eruptions in the Holocene epoch. Heimaey, the largest island in the group and the only inhabited one, also contains some material from the Pleistocene era. The most prominent feature on Heimaey before 1973 was Helgafell, a 200 metre (650 ft) high volcanic cone formed in an eruption about 5,000 years ago. The Vestmannaeyjar archipelago was settled in about 874 AD, originally by escaped Irish slaves belonging to Norse settlers on the mainland. These settlers gave the islands their name, Ireland being west of mainland Scandinavia. Although plagued by poor water supplies and piracy during much of its history, Heimaey became the most important centre of the Icelandic fishing industry, having one of the few good harbours on the southern side of the country, and being situated in very rich fishing grounds. Since the settlement, no eruptions had been known to occur on the islands until 1963, when a new member of the archipelago, Surtsey, was formed by a four-year eruption which began offshore about 20 kilometres (12 mi) south-west of Heimaey. However, offshore eruptions may have taken place in 1637 and 1896. Scientists have speculated that volcanic activity in the archipelago may be increasing due to the southward propagation of the rift zone which crosses Iceland. [edit]The eruption begins At about 20:00 on 21 January 1973, a series of small tremors began to occur around Heimaey. They were too weak to be felt by the residents of the island, but a seismic station 60 kilometres (37 mi) away, near the mainland, recorded over 100 large tremors between 01:00 and 03:00 on 22 January that appeared to be emanating from south of Heimaey. The tremors continued at a reduced rate until 11:00 that day, after which they stopped until 23:00 that evening. From 23:00 until 01:34 on 23 January, seven tremors were detected that grew shallower and more intense, while the epicenter moved closer to the town of Vestmannaeyjar. [2] The largest tremor measured 2.7 on the Richter scale. Small tremors are very common at plate boundaries, and nothing here indicated that they heralded a major eruption. The onset of the eruption was therefore almost entirely unexpected. At about 01:55 on 23 January, a fissure opened up on the eastern side of the island, barely a kilometre away from the centre of the town of Heimaey, approximately 200 metres (650 ft) east of Kirkjubær (Church farm), where the island's church had once been located. The fissure rapidly extended from 300 metres to a length of 2 kilometres (1.2 mi), crossing the island from one shore to the other. Submarine activity also occurred just offshore at the northern and southern ends of the fissure. Spectacular lava fountaining 50 to 150 metres high occurred along the whole fissure,[2] which reached a maximum length of about 3 kilometres (1.9 mi) during the first few hours of the eruption, but activity soon became concentrated on one vent, about 0.8-kilometre (0.50 mi) north of the old volcanic cone of Helgafell and just outside the eastern edge of the town. During the early days of the eruption, the rate of lava and tephra emission from the fissure was estimated to be 100 cubic metres per second (3,500 cubic feet per second), and within two days, the lava fountains had built a cinder cone over 100 metres (330 ft) high. The name initially given to the new volcano was Kirkjufell (Church Mountain), owing to its proximity to Kirkjubær. This name was not adopted by the official Icelandic place-naming committee, who chose Eldfell (Fire Mountain) instead, despite local opposition. The fountains’ Strombolian eruptions continued until 19 February, depositing thick tephra over the northern half of the island and adding to the cone until it was 200 metres (660 ft) high. [3] The eruption column that caused the air fall “occasionally rose to 9,000 metres (30,000 ft), or nearly to the tropopause”.[2] Lava flows from the cone traveled north and east to produce a “continuously expanding lava delta” along the east coast of the island and into the harbor,[3] where small explosions built up a diminutive island that was soon overtaken by the advancing delta.[2] "the viscosity of the lava fragments ejected by the blasts was, for basalt, relatively high. Very little spatter was produced and scoria bombs sometimes broke up explosively in flight (presumably due to rapid vesiculation), and by rapid impact on landing."[3] The high viscosity led to a "massive, blocky ?a?a lava flow which moved slowly but relentlessly toward the north, northeast, and east." [
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.