The glacial river Hvítá has eroded an impressive gorge into the edge of the highland where it descends from the Central highland onto the Southern lowlands along faults trending north-northeast. The Hvítá gorge is 2500 m long and its maximum depth is 70 m. The waterfall of Gullfoss is located at the head of the gorge. The Gullfoss is actually two separate waterfalls; the upper one has a drop of 11 m and the lower one 21 m. This photo covers Havítá gorge and the lower waterfall. Although the total drop is only 32 m, it is magnificent to see the large amount of glacier milk flow down through a 110 m wide waterfall. You can imagine the scale compared with figures at the upper light corner. Together with Thingvellir and the geysers of Haukadalur, Gullfoss forms the Golden Circle, a popular day tour for tourists from Reykjavík. (Photograph & Explanation: Motomaro SHIRAO)
Ever since the term stromatolith was first coined by Kalkowsky in 1908, research studies on stromatolites have continued for more than a century. This article reviews the study history of living and fossil stromatotelites. The history is divided into two parts by the discovery in 1961 by Logan of living stromatolites in Shark Bay, Western Australia, because this determined the subsequent main trend of studies on both living and fossil stromatolites. Major contributions during the last three decades include documentation of (1) a worldwide bloom of stromatolites in Proterozoic low-middle lateral shallow seas, and (2) oxygen-producing cyanobacterial activity related to stromatolites from the 1990s, resulting in various new aspects being clarified, which include in-vitro cultivation gradually revealing cyanobacterial calcification and dome-formation. Future studies will be directed towards reconciling morphological disparities and formation mechanisms among fossil, living, and cultured stromatolites.
The possibility of dynamic failure and deterioration of the sealing capacity of critically stressed rock due to the infiltration of a compressible non-wetting phase fluid is examined through laboratory experiments. Rock samples were regarded as critically stressed under normal faulting conditions, and was set up to mimic the conditions of the cap rock just above a reservoir layer. Two kinds of external stress conditions were applied to the sample, i.e., close to an isotropic stress condition and close to a critical condition for failure. Air in a gas accumulator was infiltrated into the sample from the bottom end. Axial and circumferential strains of the sample and air pressure at the inlet were monitored during the experiment. Experimental results showed that the sample under stress conditions close to the critical condition became more deformable, resulting in failure, while that under a hydrostatic condition did not deform significantly and behaved elastically. An increase in the permeability of the critically stressed sample was also suggested. Understanding an in-situ stress state and considering a possible progressive failure of the cap rock are considered to be important when evaluating sealing capacity.
This study investigated the relation between long-term changes in springwater temperature and land-use in Tokyo, as well as recent changes in springwater temperature during the period 2006–2011. Field surveys were conducted at 26 springs in Tokyo in both dry and wet seasons. Long-term changes in springwater temperature were statistically tested at each spring from the end of the 1980s until 2011 using Mann-Kendall rank statistics. Then, the relation between springwater temperature and land-use change was analyzed as follows. First, the recharge area of each spring was estimated by comparing calculated base runoff and observed discharge in the 1990s, along with the distribution of groundwater level in 1968. Next, changes in land-use between 1994 and 2000–2001 at each recharge area were calculated. A comparison with data obtained before 2006 confirmed that many springs showed a significant upward trend in springwater temperature both in dry and wet seasons. The results showed that the ratio of change from rural land-use to urbanized land-use had a positive correlation with the upward trend of springwater temperature. In addition, a negative correlation was found between the ratio of urbanized land-use in 2000–2001 and an upward trend of springwater temperature. Therefore, the authors concluded that the change of water temperature correlated more strongly with the ratio of change to urbanized land-use, rather than the ratio of urbanized land-use itself.
The northern coast of Ariake Bay, which is part of the Tsukushi Plain in Kyushu, Japan, is underlain by thick Quaternary deposits. However, the Late Middle Pleistocene succession had not been found. Recently, the Middle Pleistocene formation (Shagarami Formation) including a tephra bed (Shagarami tephra) was discovered under Aso-3 tephra in a drill core from a site near the mouth of Rokkaku River. This study revealed sedimentary facies of the Shagarami Formation, petrographic characteristics and LA-ICPMS-FT age of the Shagarami tephra. The Shagarami Formation can be divided into two sequence units on the basis of sedimentary facies, and it contains oyster fossils and mud-drape indicative of deposition in marine environments. The Shagarami tephra found in the top of the lower part of the Shagarami Formation mainly comprises pumice, and a zircon LA-ICPMS-FT age of 0.33 ± 0.06 Ma (1σ) was obtained. Therefore, lower and upper parts of the Shagarami Formation were deposited in different marine transgression and regression sequences in the Late Middle Pleistocene, respectively.
SAR interferometry is widely used for dense measurements of surface displacements caused by earthquakes, but the method cannot be applied if displacements are too large. The near-epicentral area of the Iwate–Miyagi Nairiku Earthquake in 2008 is an inapplicable case. Therefore, we applied photogrammetry to measure surface displacement caused by the earthquake. The maximum horizontal and vertical displacements were found to be 5.3 m and 2.9 m, respectively. We recognized three lines where displacement changes abruptly. The displacement distribution is like that of a reverse fault along the first line (A–B), an east-rising fault along the second line (F–G–H; west of line A–B), and a left-lateral fault along the third line (B–C; between line A–B and line F–G–H). The earthquake source fault reaches or approaches the ground surface at line A–B, with slippage decreasing toward the ground surface. The fault-like large surface deformation found north of the Aratozawa Dam is on the first line. The fault-like deformation was caused by the motion of the earthquake source fault, and the relative displacement of the fault-like deformation was enlarged by local causes. A gravitational mass movement found north of the fault-like deformation is one cause. Because the width of the rising area is small, only 3.5 km, at the southwestern side of line B–C, the slip of the earthquake source fault is mainly distributed near the ground. Line F–G–H suggests the existence of a geological structure that causes the abrupt changes of vertical displacement without a horizontal displacement, for example a high-angle fault. We assumed: (1) the slip on the main fault is distributed only in a shallow area at the southern part of the main fault and only in a deep area at the northern part; and, (2) the difference of slip caused two lateral faults between southern and northern parts. The assumption qualitatively explains many observation results, such as why there is an abrupt change of horizontal displacement along line B–C and why line F–G–H has a convex part to the east. We found a correlation between the occurrence of large landslides and abrupt changes of displacement, in other words large surface strain. The following mechanisms are possible causes of the correlation: (1) stress from surface strain increased large landslides; (2) faults (not only the main fault) may exist under the focused areas, rupture of faults caused both large surface strain and large seismic motion, and seismic motion induced large land slides. We also found that landslides and slope failures occurred densely over the slipping area on the main fault, based on the assumptions in the previous paragraph. Because photogrammetric measurements need interactive observations, we could avoid observations on possible embanking areas. Because photogrammetry allows intensive measurements at interesting areas, we revealed a two flexure-like distribution of vertical displacement. Therefore, photogrammetry is an effective method for measuring surface displacement caused by an earthquake.
We estimated the leaf area index (LAI) of Cryptomeria japonica in Aso district, Kumamoto Prefecture using various methods. In advance, we selected seven sites, which had various values of the normalized difference vegetation index (NDVI), by analyzing satellite imagery (ALOS/AVNIR-2) of September 2006. Around the end of August 2007, we measured the diameters of breast height (DBH) and tree heights at these sites, which were substituted to the universal allometric equation to calculate the dry weight of leaves of Cryptomeria japonica, proposed by Hosoda and Iehara (2010). We then estimated LAI by assuming a typical histogram of green leaf diameters of Cryptomeria japonica. At the sites, we also measured LAI using LAI-2000 and took hemispheric photographs, from which we calculated LAI using LIA32. We also estimated LAI using NDVI calculated from ALOS/AVNIR-2 imagery. Theoretically, indirect estimations of LAI-2000 and hemispheric photographs must be smaller than the allometric LAI; however, at sites with a smaller DBH, indirect estimations were larger than direct ones. This implies the possibility that the allometric equation is not suitable for estimating LAI in densely planted forest stands with a smaller DBH. In addition, we demonstrated that we should measure DBH and tree height of broader trees more accurately to estimate LAI with the equation of Hosoda and Iehara (2010), based on a simple numerical simulation.
We propose Shazam stratigraphy as a new analytical method based on facies analysis and sequence stratigraphy. This method is applied to a recently developed borehole database and subsurface geology in the Osaka Plain. Using the method, the shapes of lithofacies boundaries in subsurface sections are optimized for sedimentary faces and changes. The optimized boundary allows interpretation of seismic sections. The result is better recognition and reconstruction of depositional systems, geomorphological evolution, and tectonics. Irregular sequence boundaries, flat transgressive ravinement surfaces, and sawtooth downlap surfaces of the prograding depositional system are key boundaries for this method.
Glacier Bay in Alaska is one of the best places to observe Silurian strata formed at a shallow, tropical carbonate margin adjacent to a deep marine basin. The very thick Silurian represents a distinctive facies change from fossiliferous shelf limestone to basinal shale which is well exposed along the glaciated outcrops at Glacier Bay. The rocks are part of the far-travelled Alexander terrane, and many of the fossils are exotic to ancestral North America (Laurentia).