Question: tephra that is finer than 2 mm in diameter is called
[{'answer': 'Volcanic ash', 'provenance': [{'wikipedia_id': '47863556', 'title': 'Volcanic ash', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 12, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '47863556', 'title': 'Volcanic ash', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 880, 'bleu_score': 0.985764216565234, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 610211314853055389}, 'section': 'Section::::Abstract.'}]}]