Landslide-induced wave in a small volcanic lake: Kasu Tephra Cone,Papua New Guinea

The south crater wall of a Quaternary tephra cone in the Highlands of Papua New Guinea collapsed on 20 April 1999 and sent a 150,000-m ³ landslide into its lake. Displacing 5–10% of the lake's volume, the landslide induced a 15-m-high wave which flattened vegetation throughout the crater interior, and broke over a low saddle in the crater's east rim where it destroyed two houses and injured 11 people, killing one.     

A Flare-Triggered Heating of a Quiescent Filament

Using data obtained with the 20-cm H full-disk telescope at Big Bear Solar Observatory and Fexii 195 Å EIT on SOHO, we analyze a sudden disappearance event of a quiescent filament in detail. The filament was located along the common boundary of the active regions NOAA 9672 (S19 E13) and NOAA 9673 (N03 E18). The filament disappeared during a time interval between 17:59 UT and 19:47 UT on 22 October 2001 immediately after the onset of a major flare, which occurred in the active region NOAA 9672. At about 23:23 UT of the same day, the filament began to reappear in H and, after about 15 hours, the filament recovered to its steady state with its size being slightly smaller than that before its disappearance. This filament disappearance event belongs to the thermal type of sudden filament disappearances, which is caused by an input of additional heat. The heating mechanism that leads to sudden thermal disappearances of quiescent filaments is still not well understood. This simple event, due to the explicit cause and effect relationship between the flare and the disappearance of the filament, shows us that the flare triggered some kind of heating mechanism which continued several hours. The heat may come from the flare via heat conduction from its ribbon or from the excitation of dissipating Alfvén waves. However, from the data analysis, we conclude that the flare triggered an in-situ heating, which is likely caused by magnetic reconnection.     

Infrared Signatures of Microbreaking Wave Modulation

Infrared (IR) imagery of microbreaking waves in the ocean and laboratory showed modulation of breaking by swell and paddle-generated waves, respectively. Skin temperature also was modulated by the long waves, with the maxima occurring on the rear face of the long waves in both the laboratory and the field. The IR imagery from the ocean and laboratory showed that long-wave-induced microbreaking occurred at or near the long wave crest, and the resulting warm wakes occurred on the rear face. Thus, microbreaking waves generated near the crest of low-amplitude long waves can produce modulation with the maxima on the rear face. This mechanism was shown to be responsible for modulation of the measured in the laboratory and also likely contributed to the modulation observed in the field.     

The Tails of Externally Illuminated Young Stellar Objects in the Orion Nebula

Recent observations of externally illuminated young stellar objects in the Orion Nebula show that they have a variety of morphologies. In particular, long thin tails which terminate in points have been observed. Mechanisms will be considered here to understand the formation and properties of these tails.     

Metamictization and U-PB isotopic discordance in single zircons: a combined Raman microprobe and SHRIMP ion probe study

Summary We report results of a combined SHRIMP ion microprobe and Raman microprobe study of the correlation between metamictization and U-Pb isotopic discordance of zircon. The spatial resolution of the SHRIMP and Raman probe used are about 200 m³ and 80 m³, respectively. This allows a direct comparison of U-Pb isotopic discordance and metamictization of small areas within zircon crystals. We show that the impact of the oxygen ion beam on the zircon during the SHRIMP analysis does not cause significant amorphization or recrystallization in the remaining zircon on a scale of 1 m. Consequently, it is possible to determine the initial degree of metamictization of zircon within and adjacent to a SHRIMP analytical spot by Raman microprobe measurements after performing SHRIMP analyses. A combination of the two microprobe techniques gives information on the concentration and distribution of radionuclides as well as the degree of metamictization and its heterogeneity and the lateral age distribution within the grain. We found that the degree of U-Pb isotopic discordance correlates closely with the degree of metamictization within single zircon grains, on a scale of 15 m, which is consistent with previous results on the scale of single and multiple zircon grains showing that metamictization enhances the relative potential for secondary loss of radiogenic lead in zircon.

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Metamiktisierung und U-Pb-Isotopendiskordanz in Einzelzirkonen: eine komplexe Untersuchung mittels Ramanmikrosonde und SHRIMP Ionensonde

Zusammenfassung Wir präsentieren die Ergebnisse einer Untersuchung des Zussammenhangs von Metamiktisierung und U-Pb Isotopendiskordanz in Zirkonen mittles kombinierter SHRIMP-Ionenmikrosonden- und Ramanmikrosondenanalysen. Die räumliche Auflösung der verwendeten Analysensysteme, experimentell mit 200 m³ (SHRIMP) und 80 m³ (Ramansonde) bestimmt, gestattet den direkten Vergleich der in Mikrobereichen innerhalb von Zirkon-Einkristallen gemessenen Isotopendiskordanzen und Metamiktisierungsgrade. Wir zeigen, daß der während der SHRIMP-Analyse auf den Zirkon einwirkende Sauerstoffionenstrahl weder signifikante Amorphisierung noch Rekristallisation des benachbarten Zirkonmaterials im 1 m-Bereich hervorruft. Es ist deshalb möglich, den Grad der Metamiktisierung eines Zirkon-Mikrobereiches auch in den SHRIMP-Analysengrübchen, d.h. erst nach dem Analysieren dieses Bereiches mit der Ionensonde, mittels hochauflösender Ramanmessungen unverfälscht zu bestimmen. Der Einsatz beider Mikromethoden liefert kombinierte Informationen zu den Gehalten und Verteilungen radioaktiver Elemente, zum Grad der Metamiktisierung und seiner Heterogenität und zur lateralen Altersverteilung innerhalb von Einzelkörnern. Wir weisen eine deutliche Korrelation des Grades der U-Pb-Isotopendiskordanz mit dem Grad der Metamiktisierung im Mikrobereich (15 m Auflösung) nach. Dies stimmt mit früheren, an Einzelzirkonen und Populationen getätigten Beobachtungen überein, daß die Metamiktisierung von Zirkon dessen Potential zu sekundären Bleiverlusten erhöht.