Formation experiments of CO2 hydrate chimney in a pressure cell

Experimental investigations were conducted to understand the formation process of CO_2 hydrate the chimney structure by using a gas bubble emission technique in water within a pressure cell. The detailed process was video-recorded and analyzed to study the initiation and growth behavior of hydrate chimney while the cell pressure was increased and gas supply rate decreased gradually with time. In the initial stage of chimney growth, a hydrate crystal started to form in a cup shape at the gas nozzle and ascended together with gas bubbles due to mechanical weakness of the hydrate/nozzle contact. Growth of hydrate chimney occurred with supercooling of 3K(overpressure of 0.60MPa) or more, and continued until the top end was closed completely by hydrate

Experimental results on the formation of hard compacted snow in Rikubetsu in northern Japan: A first step toward the construction of a compacted-snow runway on the Antarctic ice sheet

This paper describes the experimental methods and results on the formation of hard compacted snow in Rikubetsu in northern Japan during the winter of 1999. This basic research was the first step towards the construction of a compacted-snow runway on the Antarctic ice sheet. In Rikubetsu, we constructed three test fields(20m in length, 7m in width, and 0.4-1.0m in thickness) on compacted basal snow(approximately 0.05m in thickness). First, 0.1-0.35-m-thick layers of snow were deposited on the basal snow of the fields using a rotary snowplow. Next, the surface snow was smoothed using an excavator. Finally, the snow layers were compacted four times using a bulldozer. This entire process was repeated three to four times in order to construct 0.4-1.0-m-thick test fields. The ram hardness, snow density, and snow structure of these fields were investigated. A comparison with the criteria established by a U.S. scientist for a large aircraft-such as the C-130(Abele, 1990)-revealed that if snow in the form of three 0.2-0.25-m-thick layers is compacted four times by a bulldozer, it is sufficiently hard to serve as a runway at H68(69°11\u279″S, 41°03\u2734″E, 1204m a.s.l.) for a wheeled C-130. The Japanese Antarctic Research Expedition plans to conduct a feasibility study on the construction of the hard com-pacted-snow runway at this location

Cloudy band observations for annual layer counting on the GRIP and NGRIP, Greenland, deep ice core samples (scientific note)

Cloudy band stratigraphy was observed in the GRIP and NGRIP, Greenland ice cores. Gray value profiles obtained from the photographic recording were analyzed to extract annual layer signals. Simple counting of gray value peaks is effective enough when annual layer thickness is relatively small (smaller than approximately 20 mm), but smoothing of the gray value profile is needed when annual layer thickness is larger. Smoothing can be done by adopting a running mean over a range of half of annual layer thickness estimated from ice flow modeling. A comparison of the DEP profile with the gray value profile revealed that the DEP profile seems to reflect the seasonal variation in general, but not exactly

Mechanical anisotropy of deep ice core samples by uniaxial compression tests (scientific paper)

Mechanical anisotropy of ice core samples has been observed in various uniaxial compression tests. The c-axis orientation distribution is the primary influence on the mechanical behavior of ice cores. A strong single-maximum fabric pattern is observed in the deep parts of the ice sheet. In this region, polycrystalline ice is very hard along the vertical axis; however, it easily shears along the horizontal plane. Thus, by acquiring the distribution of c-axis orientations throughout the ice sheet, the mechanical anisotropy of ice sheet flow behavior can be understood. Analysis of fabric measurements on the Dye 3, GRIP, and Dome F ice cores suggests that the c-axis orientation distribution depends primarily on vertical strain. Therefore, if the ice thickness at some point in the ice sheet is known, it should be possible to predict the distribution of c-axis orientations at that depth. Uniaxial compression tests were carried out along various directions of the Dye 3, GRIP, and Dome F ice cores. A contour map of mechanical anisotropy was then made to relate the compression direction to the vertical strain. This clarified the flow enhancement factor in every compression direction at a given vertical strain

The effect of hydrostatic pressure on crack formation in ice single crystals

Many tiny cracks are observed near the surface of deep ice cores drilled from polar ice sheets. These cracks probably form during the ice core drilling process at hydrostatic pressure, which increases linearly with depth. We studied crack formation in ice experimentally by deforming ice single crystals using a uniaxial compression apparatus with controlled hydrostatic pressure. The uniaxial compressive stress was applied to ice samples under a hydrostatic pressure of 20 MPa at -18℃. A constant strain rate was set at ∿(10)^s^. The c-axis orientations of the ice single crystals were parallel to the compression axis. The compression test results show that cracks formed in ice samples at a stress level of over 15MPa after 0.5% compressive strain, except for samples that deformed non-uniformly. These cracks grew along basal and parallel planes to the c-axis. This result suggests that the tiny cracks at the surface of ice cores could originate in local high stress just under the tip of the cutter

Microscopic observations on microtomed surface of ice

Surface hollows appearing after microtome shaving were observed on poly-and single crystal specimens under an optical microscope in a cold room laboratory. Characteristic shell-shaped hollows appeared with their major axis perpendicular to the shaving direction. Fewer hollows appeared at specimen surfaces when the basal plane of the ice crystal was parallel or perpendicular to the specimen surface. The results observed could be easily interpreted if cleavage cracks form parallel or perpendicular to the basal plane near the blade edge during the microtome shaving process