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Question: Please answer all the following questions correctly since they are related to the graph. There is...

Please answer all the following questions correctly since they are related to the graph.

There is geological evidence for numerous catastrophic floods during the Pleistocene. Pluvial lakes (characterized by rainfall) spilled over and eroded their natural dams; ice-dammed lakes similarly burst. For example, the Snake River in Idaho was filled to a depth of >100 m when Lake Bonneville overflowed a natural dam in northern Utah. These floods contributed to some of the greatest non-glacial instances of landscape change (such as the channeled scablands) during the Pleistocene.

Figure: Record of Holocene floods in Arizona and glacial advances around the world, including the Little Ice Age [Scott Miller, ref. unknown].

1- Examine the figure above, are floods in Arizona more common during periods of glacial expansion or retreat?

2- The Kuray and Platovo dunefields in the Altai and Sayan Mountains of southern Russia are composed of gravel, fluvial dunes up to 10 m in height. They record large discharge floods that occured 12,700 ± 2000 and 17,900 ± 1700 years ago, respectively. Pluvial Lake Bonneville catastrophically drained in a flood ~15,000 year ago. Glacial Lake Missoula burst numerous times, flooding large expanses of eastern Washington State. One such flood was ~14,000 years ago. Do megafloods generally occur during periods of time that are glacial (including deglacial) or interglacial?

Explanation / Answer

1. The floods in Arizona are more common during periods of glacial expansion. Except for one instance (3600-3000 yrs BP) in all the other four periods of glacial expansion (4800-4400 yrs BP, 2200-2000 yrs BP, 1200-800 yrs BP, and 600-200 yrs BP), the number of floods have been increasing in number, as shown in the fig.

2. Megafloods generally occur during the glacial (including deglacial) periods. All the megafloods mentioned in the question occurred during the last glacial period that lasted from 110,000 to 11,700 years ago.

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