Paleomagnetic dating of prehistoric lava flows from the urban district of Catania (Etna volcano, Italy)

Determining the ages of past eruptions of active volcanoes whose slopes were historically inhabited is vitally important for investigating the relationships between eruptive phenomena and human settlements. During its almost three-millennia-long history, Catania—the biggest city lying at the toe of Etna volcano—was directly impacted only once by the huge lava flow emplaced during the A.D. 1669 Etna flank eruption. However, other lava flows reached the present-day Catania urban district in prehistoric ages before the founding of the city in Greek times (729/728 B.C., i.e., 2679/2678 yr B.P.). In this work, the Holocene lava flows of Barriera del Bosco, Larmisi, and San Giovanni Galermo, which are exposed in the Catania urban district, were paleomagnetically investigated at 12 sites (120 oriented cores). Paleomagnetic dating was obtained by comparing flow-mean paleomagnetic directions to updated geomagnetic reference models for the Holocene. The Barriera del Bosco flow turns out to represent the oldest eruptive event and is paleomagnetically dated to the 11,234−10,941 yr B.P. and 8395−8236 yr B.P. age intervals. The mean paleomagnetic directions from the San Giovanni Galermo and Larmisi flows overlap when statistical uncertainties are considered. This datum, along with geologic, geochemical, and petrologic evidence, implies that the two lava flows can be considered as parts of a single lava field that erupted in a narrow time window between 5494 yr B.P. and 5387 yr B.P. The emplacement of such a huge lava flow field may have buried several Neolithic settlements, which would thus explain the scarce occurrence of archaeological sites of that age found below the town of Catania.

Supplemental Material: Paleomagnetic dating of prehistoric lava flows from the urban district of Catania (Etna volcano, Italy)

Figures S1–S3; Supplemental Material S4; Table S1.

Supplemental Material: Paleomagnetic dating of prehistoric lava flows from the urban district of Catania (Etna volcano, Italy)

Figures S1–S3; Supplemental Material S4; Table S1.

Recent eruption history inferred from eruption ages of the two latest lava flows using multi-dating at Yokodake Volcano, Japan

Reconstruction of the eruption history of an active volcano is necessary to elucidate its volcanic activity and to assess the probability of its volcanic eruption. Yokodake volcano in central Japan is the only active volcano among the Yatsugatake volcano group. It has effused nine lava flows, most of which have not been dated. For this study, we ascertained the eruption ages of the latest lava (Y9) and second most recent lava (Y8) using radiocarbon (14C), thermoluminescence (TL), and paleomagnetic dating methods. Results revealed the eruption ages of the two lava flows and the recent eruption history of Yokodake volcano. Yokodake volcano effused its Y8 lava flow at ca. 3.4 ka, ejected NYk-2 tephra with explosive eruption at ca. 2.4–2.2 ka, and effused the Y9 lava flow associated with Y9-T tephra at ca. 0.6 ka. Magma eruption rates of Yokodake at 34 ky and 3.4 ky were estimated as about 9 × 10−3 km3/ky and 1 × 10−2 km3/ky, indicating a stable eruption rate maintained during the past 34 ky. This result suggests that Yokodake volcano retains some potential for eruption, although the volcanic activity of the Yatsugatake volcanoes (10−1–10−2 km3/ky) has weakened over time.

Magnetic dating of the Holocene monogenetic Tkarsheti volcano in the Kazbeki region (Great Caucasus)

The radiocarbon technique is widely used to date Late Pleistocene and Holocene lava flows. The significant difference with palaeomagnetic methods is that the 14C dating is performed on the organic matter carbonized by the rock formation or the paleosols found within or below the lava flow. On the contrary, the archaeomagnetic dating allows to date the moment when the lava is cooling down below the Curie temperatures. In the present study, we use the paleomagnetic dating to constrain the age of the Tkarsheti monogenetic volcano located within the Kazbeki Volcanic Province (Great Caucasus). A series of rock-magnetic experiments including the measurement of hysteresis curves, isothermal remanence, back-field and continuous thermomagnetic curves were applied. These experiments indicated that Pseudo-Single-Domain Ti-poor titanomagnetite is responsible for remanence. A characteristic remanent magnetization was obtained for all twenty analyzed samples yielding a stable single magnetization component observed upon both thermal and alternating field treatments. Comparison of the mean directions obtained (Inc = 48.6º, Dec = 6.4º, A95 = 4.0° and K = 67) with the SCHA.DIF.14k model yielded two main time intervals (4740–4650 or 4427–4188 BC) as the best age estimate of the Lesser Tkarsheti lava flow. These results suggest an earlier age (between approximately 200 and 700 years) for this monogenetic lava flow than expected from the estimated age provided by a former 14C dating obtained in 1973 on woody remains. This first attempt to use the archaeomagnetic technique in the Caucasus indicates that the SCHA.DIF.14k geomagnetic model may be successfully used for dating purposes in the region .

Eruption age of Kannabe volcano using multi-dating: Implications for age determination of young basaltic lava flow

We estimated the eruption age of Kannabe volcano, located in southwestern Japan. Although the eruption age had been estimated using tephrochronology and K-Ar dating, the precision of its age determination left some room for improvement. The latest eruption age of Kannabe volcano is well constrained by wide spread tephras to ca. 7.2–30 ka. We applied paleomagnetic dating to a basaltic lava and optically stimulated luminescence (OSL) dating to a soil layer, which are associated with the Kannabe volcano. The soil layer above the Kannabe scoria was newly dated to be 21 ± 6 ka, as inferred from OSL dating. We also made paleomagnetic investigation to estimate the eruption age of the Kannabe basaltic lava. Paleomagnetic data of 23 rock samples from six locations in the Kannabe basaltic lava showed good mutual agreement. The average of remanent magnetizations yields declination of 0.3° and inclination of 65.9° with 95% confidence limit of 2.7°. This paleomagnetic direction with a relatively steep inclination is thought to be correlated with the paleomagnetic secular variation data of sediments in Lake Biwa at ca. 21.5 ka. Based on that information from multi-dating, we inferred that the Kannabe volcano erupted at ca. 22 ka. This result presents profound scientific implications for the precise age determination of young basaltic lava flow, for which few dating methods exist.