Here's why:
* Short vowel sounds are typically found in closed syllables, where the vowel sound is followed by a consonant. In "crunch," the vowel "u" is followed by the consonants "n" and "ch."
* Long vowel sounds often occur in open syllables, where the vowel sound is at the end of the syllable or followed by a vowel.
The "u" in "crunch" has a short, "uh" sound, typical of a short vowel.