Why do fast-moving rivers cut deep valleys?

Rivers begin high up in the mountains so they flow quickly downhill eroding the landscape vertically. Hole this helps!!

"Rivers begin high up in the mountains so they flow quickly downhill eroding the landscape vertically. The river cuts a deep notch down into the landscape using hydraulic action, corrasion and corrosion".

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read the sentence below and answer the question that follows. one of the norms in the village was to meet at the town square on fridays for a community dinner and dance. the underlined word in the sentence above is best defined as a a. cultural element shared by all people around the world b. specific area in a town used for traditional community events c. religious custom accepted and practiced by all members of a village d. behavioral pattern that is regularly accepted by a group of people