Pliny, a third source for this volcanic event, is, unfortunately, chronologically chaotic. At HN 2.202 in recording the emergence of islands from the sea, he mentions such ‘examples’ as Delos, Rhodes, Anaphe, Neae, Halone, and “Thera and Therasia among the Cyclades in the 4th year of the 135th Olympiad; also in the same group Hiera, also known as Automate, 130 years later. … “ The assertion that Thera and Therasia emerged from the sea in 237 B.C. is patently absurd. Yet this ‘event’ is said to have been followed by the emergence of “Hiera-Automate” in 107 B.C.
Editors of Pliny have attempted to alleviate this confusion by emending the “4th year of the 135 th Olympiad” to the “4th year of the 145th Olympiad,” thereby having Thera and Therasia ‘emerge’ in 197 B.C. Although this is still nonsensical, it does have the virtue of introducing the date of 197 B.C. into Pliny’s narrative. It thus becomes possible to salvage something from the text: for one can argue that Pliny was indeed aware of the emergence of a landmass in this region of the Cyclades in 197 B.C. but pointed incorrectly to Thera and Therasia, leading him to misdate the emergence of Hiera-Automate, which is more probably the landmass that emerged in the Theran caldera ca 197 B.C. This explanation seems supported by HN 4.70, in which Pliny writes of Thera, called Calliste when it first emerged, Therasia, which afterwards was torn away from it, and inter duas the soon born Automate, also called Hiera. The general sequence of events seems correct, even if the dates are not; thus Pliny’s text, despite its chronological problems, is valuable for providing the actual name of the first island to rise out of the caldera: Hiera, or Automate. Moreover, like Strabo and Seneca, Pliny leads his reader to believe that this island still existed in his own day, as Plutarch confirms. …
The data provided by the ancient sources suggest the following reconstruction of the history of Hiera: its birth was marked by a subaerial eruption that took place in the caldera in the 145th Olympiad, perhaps in 198 or 197 B.C.; over the four days of this eruption the island grew into a landmass with a perimeter of ca 2.2 km; Rhodian sailors were eye-witnesses to this event, and not only erected a shrine to Poseidon on the new island, but also carried the news of its existence back to Rhodes; the island continued to exist into the eighth century, when it was in fact enlarged by another eruption. There is no reliable ancient evidence that Hiera was submerged or disappeared in GrecoRoman antiquity.
Seneca (Q Nat 2.26.4ff) attests that at least one other volcanic landmass appeared in the Theran caldera during the Julio-Claudian period: immediately after describing Posidonius’ second-century B.C event, Seneca adds that” the same thing happened again in our own time [nostra memoria] during the second consulship of Valerius Asiaticus” (in 46). This assertion is indeed repeated a second time at Q Nat 6.21.1: “Does anyone doubt that air brought Thera and Therasia into the light of day, as well as that island which in our own time was born before our very eyes [spectantibus nobis] in the Aegean Sea?” Although Seneca does not provide a name for this new island, he clearly speaks with great certainty about an event that took place during his own lifetime.
Whereas Seneca seems clear and precise, another source for this eruption, Pliny’s confused text (H N 2.202), places the emergence of an island he calls Thia 110 years after the creation of Hiera (in 67 B.C), i.e., in A.D. 43; he then contradicts himself by placing the emergence of Thia in the consulship of M. Junius Silanus and L. Balbus, i.e., in A.D. 19. Pliny’s text, in fact, gives rise to the theory that two distinct volcanic events took place in the caldera during the first century-one in 19, the other in the reign of Claudius.
The evidence for an event in 19, however, is extremely weak. Not only is its source the garbled text of Pliny, but Pliny even seems to contradict himself again by stating that the emergence of Thia took place “in our age” [in nostro aevo], a rather curious assertion for a person who lived from A.D. 28 to 79. In fact, Pliny repeats this assertion at H N 4.70, where he writes that Thia “emerged near the same islands [i. e., Thera, Thcrasia, and Automate/Hiera] in our own time [in nostro aevo],” a statcment that would make much more sense if referring to an event during the reign of Claudius.
Though Pliny’s text is chronologically nonsensical if taken at face value, there is a noteworthy mathematical progression to be found in it. If one counts the years elapsing between the Theran island of ca 197 B.C. and that of ca A.D. 46, one arrives at a figure of ca 243 years-a figure very close to the 240 years (130 + 110) recorded by Pliny (HN 2.202). It is thus plausible to argue that Pliny was aware that (1) two volcanic islands had emerged in the Theran caldera, and (2) approximately 240 years had separated these events. …
Cassius Dio and Philostratus are also pertinent. Dio notes (61.29.7) that “this year [apparently A.D. 47] a small islet, hitherto unknown, made its appearance close to the island of Thera.” This unnamed [small islet] is apparently the same island mentioned by Philostratus VA 4.34: Apollonius was in Crete when an earthquake and seismic sea wave struck the coast at Leben; to calm the populace, Apollonius told them to be of good courage, “for the sea has given birth and brought forth land.” Philostratus then goes on to record: “After a few days some travellers arrived from Cydoniatis and announced that on the very day on which this portent occurred and just at the same hour of midday, an island rose out of the sea in the firth between Thera and Crete” (Loeb translation). Given that Philostratus next refers to Apollonius moving on to Rome during the reign of Nero, it seems likely that the unnamed island born near Thera must that of ca 46. …
Eusebius provides the additional information that, during the reign of Claudius, an island of thirty stades … arose between Thera and Therasia. The Armenian version likewise records that in the fifth year of the reign of Claudius inter Theram et Therasiam exorta est insula fere stadiis XXX; similarly, Jerome refers to the emergence of an island habens stadia XXX during the reign of Claudius. Here, for the first time, the size of the new landmass is recorded, and the figure of thirty stades will be repeated in such later sources as Oras. 7.6, Cassiod. Chron. 656, Syncellus Ec. Chron. 630, and Cedrenus Ann. 347….
Aurelius Victor provides another new piece of evidence about the event of 46 (Caes. 4): in the reign of Claudius in Aegaeo mari repente insula ingens emersit nocte, qua defectus lunae acciderat. As usual, the new island is not named, but the adjective ingens seems to agree with Eusebius’ thirty stades (perhaps influenced by that source), and the island is said to have emerged during a lunar eclipse. We do know that such an eclipse took place during the night of 31 December 46 (Fouque) - an explanation of why the dates of 46 and 47 both appear in our ancient sources….
[A]lthough our theoretical composite island with a perimeter of 5,600 m. is ca 2,000 m. larger than the present-day Palaea Kameni, there is strong evidence that Palaea Kameni lost a significant amount of land in 1457. An inscription of 1457, as recorded by ROSS,[…] addressed to Duke Francesco Crispo II, attests that in 1457 a large portion of Palaea Kameni collapsed into the caldera bay. The site provides evidence of this catastrophe, for the island features a steep cliff in its southern half, facing Nea Kameni; in general appearance this cliff looks very much like a collapse structure…