CAPE 2009 P2/U1 #6 a) From the passage above, identify FOUR characteristics of a tsunami which contribute to its destructive power. [4 marks]Four characteristics of a tsunami which contribute to its destructive power are: Recession of the water leads to huge waves in excess of 20 feet in some cases. The velocity of the tsunami as it makes touchdown, is so powerful, it destroys everything in its path. The loud hissing sound of the tsunami is associated with its impact on land as it may be so powerful it modified the beach completely. The height of the water as it swept inland may have been destructive as it covered the 10 foot top of the beach ridge. b) Describe the operation of the Pacific Tsunami Warning System. [ 6 marks] The Tsunami Warning System in the Pacific has the functions of monitoring seismologicaland tidal stations throughout the Pacific Basin to evaluate potentially tsunami genic earthquakesand disseminating tsunami warning information. The Pacific Tsunami Warning Center (PTWC)is the operational center of the Pacific Tsunami Warning System. If the location and magnitude of an earthquake meet the known criteria for generation of atsunami, a tsunami warning is issued to warn off an imminent tsunami hazard. The warningincludes predicted tsunami arrival times at selected coastal communities within the geographicarea defined by the maximum distance the tsunami could travel in a few hours. A tsunami watchwith additional predicted tsunami arrival times is issued for a geographic area defined by thedistance the tsunami could travel in a later time period. Tsunami watch, warning and information bulletins are disseminated to appropriateemergency officials and the general public by a variety of communication methods. The PTWCdisseminates bulletins to local, states, international and national users as well as the medis. Theseusers, in turn, disseminate the tsunami information to the public, generally over commercialradio and television channels.
CAPE 2009 P2/U1 #6 c) Explain how climate, the characteristics of the river basin, and human activities might cause rivers to flood. [20 marks] Rivers can flood as a result of climate, characteristics of the river basin and humanactivities. These all have different root causes for which the river floods. Firstly, a river might flood because of the climate. Climate is defined as the atmosphericconditions of a geographical area over a long period of time usually 30-35 years. In the someCaribbean countries such as Trinidad and Tobago which have a distinct dry season and wetseason, can cause rivers to flood on its own. During the dry season, the precipitation levels areconsiderably lower than that of the wet season. By extension, the dry season is usuallycharacterized by temperatures exceeding on average, 32oC. Such temperatures cause severedrought in these Caribbean islands. Severe temperatures are usually accompanied by forest fireswhich in many cases remove all the tree cover in mountainous regions. When this vegetationcover is removed by forest fires, it means that it has the potential for flooding in the future. Thisis because; extremes in temperatures restrict infiltration and increase surface runoff. When thewet season arrives, and precipitation levels are once again high, increased rainfall usually causesincreased surface runoff to exceed the infiltration capacity. This results in an increase in thelevels of water in rivers hence causing rivers to flood its banks. A case in point, the 2010 dryseason in Trinidad and Tobago led to severe flooding in the wet season. Secondly, the characteristics of the river basin might cause rivers to flood. The river basinis the area drained by the river. Characteristics of the river basin include; basin size and relief. Ifa basin is small it is likely that rainfall will reach the main channel more rapidly than in a largerbasin where the water has much further to travel. This means that the river has the potential toflood where the basin size is smaller as the length of time it takes for water to reach the mainriver, may not give sufficient time for the water in the river to drain properly and it may back upand cause flooding. Additionally, the slope of the basin and its valley sides also determineswhether a river floods. In steep sided upland valleys, water is likely to reach the river morequickly than in gently sloping lowland areas. This, as a result, may cause a river to flood since;again, the river may not get enough time to drain the water. Lastly, human activities can also cause rivers to flood. Land management techniques suchas drainage systems, digging ditches, ploughing up and down a slope may also increase the riskof flooding by a river. However, urbanization and deforestation are the two most common humanactivities to increase the possibility of flooding by a river. By building new towns or increasingthe size of urban areas makes land surface impermeable. It increases the amount of runoff byremoving topsoil for construction and compacting the ground with earth moving machinery.Also, straightening river channels and lining them with concrete to enable building plans toproceed increases runoff. This leads to faster delivery of water downstream of the urban area
CAPE 2009 P2/U1 #6increasing the risk of flooding in those areas. Deforestation is also another human cause thatcauses a river to flood. The removal of trees reduces interception and evapotranspirationresulting in increased runoff and soil erosion. The eroded material finds its way into watercourses where it aggrades the river bed. This reduces channel capacity increasing the likelihoodof flooding. Deforestation in the Himalayas, the upper reaches of the River Ganges, may beincreasing the frequency of flooding in Bangladesh.