Scientists have difficulty predicting the frequency and intensity of flooding along major rivers, such as the Mississippi, because the increased run-off from impervious surfaces in large human settlements changes how much water flows into rivers.

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explanation:

explanation:

since the crust is readily accessible, scientists have been able to perform hands-on experiments to determine its composition; studies on the more distant mantle and core have limited opportunities samples. so scientists also rely on analyses of seismic waves and gravity and as well as magnetic studies.