Simulation of dimensionality effects in thermal transport

The discovery of nanostructures and the development of growth and fabrication techniques of one- and two-dimensional materials provide the possibility to probe experimentally heat transport in low-dimensional systems. Nevertheless measuring the thermal conductivity of these systems is extremely challenging and subject to large uncertainties, thus hindering the chance for a direct comparison between experiments and statistical physics models. Atomistic simulations of realistic nanostructures provide the ideal bridge between abstract models and experiments. After briefly introducing the state of the art of heat transport measurement in nanostructures, and numerical techniques to simulate realistic systems at atomistic level, we review the contribution of lattice dynamics and molecular dynamics simulation to understanding nanoscale thermal transport in systems with reduced dimensionality. We focus on the effect of dimensionality in determining the phononic properties of carbon and semiconducting nanostructures, specifically considering the cases of carbon nanotubes, graphene and of silicon nanowires and ultra-thin membranes, underlying analogies and differences with abstract lattice models.Comment: 30 pages, 21 figures. Review paper, to appear in the Springer Lecture Notes in Physics volume "Thermal transport in low dimensions: from statistical physics to nanoscale heat transfer" (S. Lepri ed.

The ages of calderas, large explosive craters and active volcanoes in the Kuril-Kamchatka region, Russia

The ages of most of calderas, large explosive craters and active volcanoes in the Kuril-Kamchatka region have been determined by extensive geological, geomorphological, tephrochronological and isotopic geochronological studies, including more than 600 14C dates. Eight ‘Krakatoa-type’ and three ‘Hawaiian-type’ calderas and no less than three large explosive craters formed here during the Holocene. Most of the Late Pleistocene Krakatoa-type calderas were established around 30 000–40 000 years ago. The active volcanoes are geologically very young, with maximum ages of about 40 000–50 000 years. The overwhelming majority of recently active volcanic cones originated at the very end of the Late Pleistocene or in the Holocene. These studies show that all Holocene stratovolcanoes in Kamchatka were emplaced in the Holocene only in the Eastern volcanic belt. Periods of synchronous, intensified Holocene volcanic activity occurred within the time intervals of 7500–7800 and 1300–1800 14C years BP

Radiocarbon dating and tephrochronology in Kamchatka

We discuss results of 14C dates obtained from areas of young volcanoes in Kamchatka. We apply these dates to reconstructing regional volcanic activity during the Holocene

Radiocarbon dating of large Holocene volcanic events within South Kamchatka (Russian Far East)

Radiocarbon dating is widely used when studying recent volcanic activity in the Kamchatka Peninsula due to the abundance of organic matter that is associated with the volcanic deposits. Here, we present the results of 14C dating of major volcanic events within the active South Kamchatka volcanic zone. South Kamchatka includes 8 recently active volcanic centers (stratovolcanoes, calderas, and large craters) that have been erupting during the Holocene. Their tephras represent useful markers for both the southern part of the peninsula and the Northern Kurile Islands. Since these marker tephra layers facilitate stratigraphic and tephrochronological studies in this area, it was important to determine their ages. We have obtained 73 new individual 14C dates on paleosol, peat, charcoal, and wood associated with the marker tephra layers, then complemented these data with 37 earlier published dates and analyzed the resulting data set. We selected the reliable dates and then obtained average 14C ages of marker tephra layers. The details of these procedures, as well as brief descriptions of South Kamchatka Holocene eruptions and their tephra beds, are presented in the paper

Holocene catastrophic caldera-forming eruptions of Ksudach volcano, Kamchatka

Four Plinian eruptions of Ksudach have been reconstructed and dated by the carbon-14 method. The eruptions produced three collapse calderas: the KS1 eruption formed Caldera V 1700-1800 years ago, the KS2 and KS3 events produced Caldera IV 6000-6100 years ago, and the KS4 eruption formed Caldera III 8700-8800 years ago. The most violent eruption was the KS1 event. The sizes of the calderas were 4 × 6.5 km (V), 5 × 6 km (IV), and presumably 2-3 km across (III). Juvenile material was erupted in a rhythmic manner. The composition of the products was dominated by andesite (KS2 and KS4), dacite and rhyodacite (KS3), and rhyodacite (KS1). It is assumed that all caldera-forming eruptions were triggered by the injection of a new portion of high-temperature basic magma and its mixing with the cooling acid magma of the preexisting source. -from Journal summar

Ages of active volcanoes in the Kuril-Kamchatka region

The births (ages) of most of the active volcanoes, calderas, and large craters produced by caldera-resembling eruptions (subcaldera craters) were dated as a result of geological, geomorphological, tephrochronological, and isotopic studies. The dated active volcanoes were found to be fairly young formations, the age of the oldest being 40-50 thousand years. Most of the presently highly active volcanoes had been born at the very end of the late Pleistocene or during the Holocene. Carbon-14 ages were determined for the majority of the Holocene volcanoes. The periods of time when Holocene volcanoes had been synchronously active were 7500-7800 and 1300-1800 years ago. -from Journal summar

Great explosive eruptions on Kamchatka during the last 10,000 years: Self-similar irregularity of the output of volcanic products

Temporal irregularity of the output of volcanic material is studied for the sequence of large (V ≥ 0.5 km3, N = 29) explosive eruptions on Kamchatka during the last 10,000 years. Informally, volcanic productivity looks episodic, and dates of eruptions cluster. To investigate the probable self-similar clustering behavior of eruption times, we determine correlation dimension Dc. For intervals between events 800 and 10,000 years, Dc ≈ 1 (no self-similar clustering). However, for shorter delays, Dc = 0.71, and the significance level for the hypothesis Dc < 1 is 2.5%. For the temporal structure of the output of volcanic products (i.e., for the sequence of variable-weight points), a self-similar “episodic” behavior holds over the entire range of delays 100–10,000 years, with Dc = 0.67 (Dc < 1 at 3.4% significance). This behavior is produced partly by the mentioned common clustering of event dates, and partly by another specific property of the event sequence, that we call “order clustering”. This kind of clustering is a property of a time-ordered list of eruptions, and is manifested as the tendency of the largest eruptions (as opposed to smaller ones) to be close neighbors in this list. Another statistical technique, of “rescaled range” (R/S), confirms these results. Similar but weaker-expressed behavior was also found for two other data sets: historical Kamchatka eruptions and acid layers in Greenland ice column. The episodic multiscaled mode of the output of volcanic material may be a characteristic property of a sequence of eruptions in an island arc, with important consequences for climate forcing by volcanic aerosol, and volcanic hazard

The 7600 (14C) year BP Kurile Lake caldera-forming eruption, Kamchatka, Russia: stratigraphy and field relationships

The 7600 14C-year-old Kurile Lake caldera-forming eruption (KO) in southern Kamchatka, Russia, produced a 7-km-wide caldera now mostly filled by the Kurile Lake. The KO eruption has a conservatively estimated tephra volume of 140–170 km3 making it the largest Holocene eruption in the Kurile–Kamchatka volcanic arc and ranking it among the Earth’s largest Holocene explosive eruptions. The eruptive sequence consists of three main units: (I) initial phreatoplinian deposits; (II) plinian fall deposits, and (III) a voluminous and extensive ignimbrite sheet and accompanying surge beds and co-ignimbrite fallout. The KO fall tephra was dispersed over an area of >3 million km2, mostly in a northwest direction. It is a valuable stratigraphic marker for southern Kamchatka, the Sea of Okhotsk, and a large part of the Asia mainland, where it has been identified as a f6 to 0.1 cm thick layer in terrestrial and lake sediments, 1000–1700 km from source. The ignimbrite, which constitutes a significant volume of the KO deposits, extends to the Sea of Okhotsk and the Pacific Ocean on either side of the peninsula, a distance of over 50 km from source. Fine co-ignimbrite ash was likely formed when the ignimbrite entered the sea and could account for the wide dispersal of the KO fall unit. Individual pumice clasts from the fall and surge deposits range from dacite to rhyolite, whereas pumice and scoria clasts in the ignimbrite range from basaltic andesite to rhyolite. Ignimbrite exposed west and south of the caldera is dominantly rhyolite, whereas north, east and southeast of the caldera it has a strong vertical compositional zonation from rhyolite at the base to basaltic andesite in the middle, and back to rhyolite at the top. Following the KO eruption, Iliinsky volcano formed within the northeastern part of the caldera producing basalt to dacite lavas and pyroclastic rocks compositionally related to the KO erupted products. Other post-caldera features include several extrusive domes, which form islands in Kurile Lake, submerged cinder cones and the huge silicic extrusive massif of Dikii Greben’ volcano