artwork is an unreliable guide to a society's behaviour, using the example that frescoes recovered prior the Late Minoan period seldom depict people interacting with each other yet this should not be taken as evidence that Minoans rarely did so. Molloy further argues that the lack of fortifications could be attributed to the Crete's rugged topography, which would have provided a significant natural defensive advantage; Molloy argues that the guardhouses could have been used to secure narrow roads through Crete. About Minoan warfare, Branigan concluded: Archaeologist Olga Krzyszkowska agreed: "The stark fact is that for the prehistoric Aegean we have no direct evidence for war and warfare per se." Collapse Between 1935 and 1939, Greek archaeologist Spyridon Marinatos posited the Minoan eruption theory. An eruption on the island of Thera (present-day Santorini), about from Crete, occurred during the LM IA period (1550–1500BC). One of the largest volcanic explosions in recorded history, it ejected about of material and was measured at 7 on the Volcanic Explosivity Index. The eruption devastated the nearby Minoan settlement at Akrotiri on Santorini, which was entombed in a layer of pumice. Although it is believed to have severely affected the Minoan culture of Crete, the extent of its effects has been debated. Early theories proposed that volcanic ash from Thera choked off plant life on the eastern half of Crete, starving the local population; however, more-thorough field examinations have determined that no more than of ash fell anywhere on Crete. Based on archaeological evidence, studies indicate that a massive tsunami generated by the Thera eruption devastated the coast of Crete and destroyed many Minoan settlements. Although the LM IIIA (late Minoan) period is characterized by affluence (wealthy tombs, burials and art) and ubiquitous Knossian ceramic styles, by LM IIIB (several centuries after the eruption) Knossos' wealth and importance as a regional center declined. Significant remains have been found above the late Minoan I-era Thera ash layer, implying that the Thera eruption did not cause the immediate collapse of Minoan civilization. The Minoans were a sea power, however, and the Thera eruption probably caused significant economic hardship. Whether this was enough to trigger a Minoan downfall is debated. Many archaeologists believe that the eruption triggered a crisis, making the Minoans vulnerable to conquest by the Mycenaeans. According to Sinclair Hood, the Minoans were most likely conquered by an invading force. Although the civilization's collapse was aided by