Retrieving geomagnetic secular variations from lava flows: evidence from Mounts Arso, Etna and Vesuvius (southern Italy)

Abstract

Summary Mean directions of magnetization from Mounts Arso (Ischia Island, Gulf of Naples), Etna and Vesuvius lava flows have been determined based on very stringent linearity criteria. These indicate that, regardless of the source volcano, the lava flow mean directions of magnetization form a common path, the SISVC (Southern Italy Secular Variation Curve). This curve enables a reassessment of the age of eruption of several lavas. A date of AD 1169 is demonstrated to be the only possible time of emplacement for one Etna lava flow previously assigned an age of AD 812/1169. It is also demonstrated that two Etna lava flows, which, according to the literature, were emplaced in AD 1536 and 1595 respectively, were actually both emplaced around AD 1037. Three other Etna lava flows, one ascribed to AD 1566 and two to AD 1595, were actually emplaced between AD 1169 and 1284/85. The same time window also holds for a Vesuvius lava flow for which only an upper time threshold was previously available. Only one of the studied flows needs further sampling and analysis to verify whether this flow has been affected by a complete remagnetization or has an erroneous historical dating. The applied procedure seems to be the most appropriate one in carrying out palaeomagnetic surveys of lava flows, as also suggested by the broad agreement with some 17th and 19th century measurements of the geomagnetic field in Rome, relocated to Etna, and is likely to improve knowledge of past history of a volcano significantly.

Chronology of Vesuvius? activity from A.D. 79 to 1631 based on archeomagnetism of lavas and historical sources

“…(c) Data set for lavas from A.D. 79 to 1631 from Carracedo et al (1993) (V) and (d) from Gialanella et al (1993 and (G) and Hoye (1981) very quickly and consequently acquire less secondary magnetisation during mechanical core sampling than "hard" samples, such as lavas. Finally, we must point out that some authors (Gialanella et al, 1993(Gialanella et al, , 1998Incoronato, 1996Incoronato, , 1999Incoronato et al, 2002) were led to incorrect conclusions on medieval lavas (Table 8) because they also used the wrong reference curve defined by Hoye (1981).…”

Comments on “Chronology of Vesuvius' activity from A.D. 79 to 1631 based on archeomagnetism of lavas and historical sources” by C. Principe et al., Bull Volcanol

“…Analysis of historical lava-flow units has revealed many cases where the ChRM direction deviated from the Earth's field. In the case of Italian volcanoes, a disagreement of a few degrees between the secular variation (SV) curve derived from historical direct measurements of the Earth's field and the lava-flow unit's remanence directions has long been pointed out in the literature (Rolph et al 1987;Incoronato et al 2002;Tanguy et al 2003) and has been shown to occur for practically all the post-1631 lavas; the ChRM direction of which can be checked against historical direct measurements (Lanza et al 2005).…”

High-resolution petrophysical and palaeomagnetic study of late-Holocene shelf sediments, Salerno Gulf, Tyrrhenian Sea

“…Resolution of palaeomagnetic data for the C836 core is only approximate for ages greater than c. 6500 years. Stars and solid symbols show, respectively, the archaeological and historical dated palaeomagnetic directions obtained in France for the last 2000 years (Bucur, 1994) and from Vesuvius and Ischia (Hoye, 1981;Gialanella et al, 1993;Incoronato, 1996;Incoronato et al, 2002). for the last 6500 years ( Figure 7A), whereas it can be only roughly estimated between c. 7000 and 9000 years, due to the poor resolution of our palaeomagnetic data in that interval. We also notice that the pronounced palaeointensity minima corresponding to AD 79 in the C836 curve ( Figure 7A) may partly be due to lithological factors.…”

“…Palaeomagnetic data from the Vesuvius and Ischia volcanic products, relocated to Vesuvius using the inclined geocentric dipole model of the Earth's magnetic field (Tarling, 1983;Noel and Batt, 1990) provide historically dated palaeomagnetic values for AD 1631 and AD 1301 (Hoye, 1981;Gialanella et al, 1993;Incoronato, 1996). Mediaeval Vesuvius lavas (Incoronato et al, 2002) provide further tie-points at AD 1139, AD 1037 and AD 968 ( Figure 7A); in general, the palaeomagnetic data from volcanic products exposed on land seem to confirm the palaeomagnetic inclination behaviour observed in the Gulf of Salerno cores, between 400 and 1032 years BP.…”