I recently asked a question Do we pronounce the vowel at the beginning of the word with a preceding glottal stop? on the English site and received a very good answer.
According to the answer on that question, English speakers usually pronounce words beginning with a vowel, with a glottal stop when following a pause. That answer explained also that [I]n Hawaiian, the distinction is phonemic i.e. /ahi/ and /ʔahi/ have different meanings. But in English, it is phonetic (allophonic).
I wonder what causes us to have a glottal stop before a vowel after some silence. What happens to our vocal cords when we start from silence? I tried to pronounce a "pure vowel" at the beginning without trying to pronounce a glottal stop but I can't do that.
What causes our vocal cords to produce a glottal stop before a vowel after some silence? Is there a phonetic (or phonological?) explanation for this?