Merrill said workers were dealing with a "very unusual sinkhole" -- deep, wide and extremely unstable.

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He said workers were dealing with a "very unusual sinkhole" -- deep, wide and extremely unstable.

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Here were bugs that created hydrazine, an extremely unstable compound, used as rocket fuel, that is poison to most living things.

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In 2009 and the years leading up to it, we had an extremely unstable dollar under Federal Reserve Chairmen Alan Greenspan and Ben Bernanke.

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Mr Murphy said the flats at Spencer Court were "extremely unstable".

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In Arkansas, wind shears and unstable weather conditions suitable for forming super cells, extremely large cloud systems capable of generating powerful tornadoes, were approaching Little Rock.

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