Halliday & Matthiessen (2014: 231-2):
‘Intransitive’ ‘creative’ clauses have the sense of ‘come into existence’ and shade into clauses of the ‘existential’ process type. One difference is the unmarked present tense: it is present–in–present for material clauses … but the simple present in existential ones. Another difference is the potential for a construction with there as Subject in existential clauses, but not in creative material ones.