Central Mountainous Areas Research Articles

Reconstructed Pleistocene Ice-Sheet Temperatures and Glacial Erosion in Northern Scotland

AbstractPleistocene ice-sheet temperatures are reconstructed for a west-to-east transect across northern Scotland at the ice maximum using the temperature-profile model of Budd and others (1971[a]). Basal freezing is predicted for the central area of the ice sheet, and zones of basal melting on each side to the west and east. Variations in estimates of annual accumulation rate and ice thickness do not greatly alter this general pattern. However, small errors in estimating mean annual temperature at the ice edge and ice-surface temperature lapse-rate may significantly change the pattern of predicted basal temperature regimes, and basal freezing may have extended over the whole of the area considered. Zones of areal scouring occur in both the west and east of the transect but are absent from the central mountain area. Under some of the temperature conditions modelled there is a partial spatial coincidence of the areal scouring in the west with predicted areas of basal melting, but almost none in the east. Possibly this is explained because glacial erosion relates to time periods other than the ice maximum.

Lodgepole Terminal Weevil 1 in Interior Lodgepole Forests

Pissodes terminalis Hopping is a widespread associate of Pinus contorta Dougl . in the central Rocky Mountain and Intermountain areas. Life history and habits are similar to those reported for the species elsewhere. Infestations are heaviest in stands in which trees are 5–20 ft tall, and decline as trees grow out of this height class. In one intensive study area about 50% of the trees had been infested at least once, some repeatedly. Dense stands are infested most frequently.

Algae from Alpine Areas in Rocky Mountain National Park, Colorado

A collection of algae from alpine lakes (above 3000 m), principally desmids and diatoms, indicates oligotrophic, somewhat acid conditions. There have been few investigations of the algae of the central Rocky Mountain area of the United States. Shantz (1907) reported a few genera of the Pike's Peak area and Robbins (1912) published a preliminary list of Colorado algae. Olive (1955) reported a number of genera and named 35 species. In an excellent limnological study, Pennak (1955) listed 42 genera of algae, including several genera we have not found, and gave notes on their abundance as well as physical data from Bear Lake which we studied. Jones (nee Hallberg) (1937, 1932) reported some blue-green species. The only papers listing a sizable number of species are those of Miller (1936), who reported 112 species of desmids from the Medicine Bow Mountains (Wyoming); Durrell and Norton (1960), who listed 81 genera and 152 species from Grand Mesa; and Thomasson's (1964) paper on some lakes northwest of Denver which lists about 100 taxa. These are regions north and southwest of Rocky Mountain National Park. Stein and Amundsen (1967) reported a few species of snow algae from the Front Range south of the Park. Apparently there are few if any species so far reported from the Park. In early September 1969, one of us (L.A.W.) had the opportunity to collect 16 samples in the Park above 9000 ft (3000 m). Plankton collections were made with a No. 25 silk plankton net in Bear, Sheep and Poudre lakes. Littoral collections were made from the three lakes and a beaver pond near Horseshoe Park, from tundra pools, Iceberg Lake and a snowbank. Collections were kept refrigerated 48 hr until they could be examined fresh in our laboratory. All were then preserved in Transeau's solution and studied in more detail later. Permanent diatom slides were made, and all samples were deposited in the University herbarium. A total of 193 taxa representing 84 genera have been identified. Bear Lake is a small natural lake at 3200 m elevation in the east central part of the Park. It is in the evergreen forest and is about 150 X 100 m in size. Water temperature was 15 C and the pH near 6.5 (Pennak reports pH 6.3-6.7). Dinobryon cylindricum was abundant in the net collection; Ceratium hirundinella was moderately abundant, and Volvox aureus common. Among the 15 genera present were species of Asterionella, Melosira, Tabellaria, Peridinium and four desmids. The littoral zone was dominated by filamentous green algae in the genera Zygnema, Spirogyra, Mougeotia, Sphaerozosma and Bulbochaete. More than 30 other species were seen, mostly Chlorococcales,

Crustal and Upper Mantle Structure in Japan from Amplitude and Phase Spectra of Long-period P-waves

Crustal and upper mantle structure in the Chugoku region has been studied by the same method as described in Part 1 of this paper, by analyzing the seismograms of long-period P-waves recorded at Shiraki. Further theoretical evaluation of the method for the dissipative and anisotropic media is made, in addition to Part 1. The observational curves of the amplitude ratio and phase difference for 25 shocks are classified into six sets by the direction of wave approach to Shiraki. The first high peaks of the curves for waves approaching from the near south to southeast direction appear at frequencies higher than those from the other directions. This suggests that the crust becomes thinner towards this direction. Comparing these observational curves with the theoretical curves, which are calculated by varying layer parameters of the models so far proposed for the structure near this region, four combinations of probable models are finally obtained and the average layer thicknesses are estimated. Among these models, model SHK70-4 is considered as most probable, whose thicknesses of the crust and 7.4km/sec intermediate layer are about 41km and 26km, respectively. However, models SHK70-2 and 3 cannot be excluded. The former, which has a crustal thickness of about 26km and the thickness of the intermediate layer of about 17km, is more probable than the latter. From travel-time studies late arrivals of P-waves at Shiraki as much as about 0.6 seconds are observed, compared with those at Matsushiro and Tsukuba. This implies that the upper mantle with a lower velocity is fairly thicker around this area than in the central mountain area and the Kanto plain.

Crustal and Upper Mantle Structure in Japan from Amplitude and Phase Spectra of Long-period P-waves Part 1. Central Mountain Area

A method is shown to study the crustal and upper mantle structure from the amplitude and phase spectra obtained from the analysis of long-period P-waves. Taking the amplitude ratio of the vertical component to horizontal one and the phase difference between them, we obtain two observational curves which depend only on the structure beneath a recording station. Comparing these curves with the corresponding theoretical ones derived from an assumption of the horizontal parallel layering of homogeneous media, we can select a most probable model in which the theoretical and observational curves fit well each other.In order to study the structure under the central mountain area, the records registered at Matsushiro have been analyzed. Among four sets of observational curves corresponding to four regions classified by the incident direction, there appear fairly remarkable differences, implying the possible lateral variations of layer interfaces. Confining, therefore, the validity of the above assumption to each of the four regions respectively, and varying layer parameters of the models so far obtained from gravity, travel time and surface wave studies, we have obtained a few probable models for each region. Taking into account all available information on the structure in this area, we have selected one model for each region. The models obtained reveal that the crustal thickness (the thickness of the intermediate layer is not included) is about 40km over this area, and that there is a thick 7.4km/sec intermediate layer whose thickness is considerably different among the four regions. Although Matsushiro is situated in the tectonic region with a thick underlying intermediate layer, surrounded by highly mountain ranges, travel-time residuals from Jeffreys-Bullen table show a remarkable negative value, suggesting the possibility of rather higher velocity in the upper mantle below the intermediate layer or/and the lack of a low-velocity layer, compared with other tectonic regions.

爆破地震動観測による東北日本を横断する測線上の地殼構造

The crustal structure in a profile crossing the northeastern part of Honshu, Japan, is derived from the data obtained in the Off Kesennuma, the Off Oga Peninsula and the Tutihata explosions. The fixed array-moving shot point technique was first applied in this profile, and more than 600 seismograms were obtained. Assuming a homogeneous layered structure, the thickness of the crust in the central mountain area was obtained as 30km. The crust tapers near the shore toward the ocean on both sides of Honshu, and the transition of crustal structure from the continental to the oceanic seems to occur in the vicinity of Honshu. The existence of the basaltic layer and the value of 8.0km/s for Pn velocity became more convincing through the analysis of this profile.

The Crustal Structure of Honshu, Japan

A model of the crustal structure of Honshu, Japan, deduced from the data obtained by the Research Group for Explosion Seismology is as follows : 1) The velocity of the shallowest layer is 5.5 to 5.8 km/sec and its thickness is less than several km. In some localities this layer does not exist and a layer with the velocity 6.1 to 6.3 km/sec is found just below surface layers.2) The depth of the Moho discontinuity is about 20 km in north-eastern area, about 25 km in Kanto, and about 35 km in the central mountainous area. These values are deduced under the assumption that the crust is mostly composed of the material with the velocity of 6.1 to 6.3 km/sec.3) The velocity of P wave below Moho discontinuity is slower than 8 km/sec.4) According to the results obtained in the recent observations in the central and Kinki areas, a layer of about 6.6 to 6.7 km/sec exists below the layer of 6.1 to 6.3 km/sec. The part of the crust between this layer of 6.6 to 6.7 km/sec and the Moho discontinuity may have the velocity bigger than 7 km.5) If we assume that a “hidden layer” of 6.6 to 6.7 km/sec exists in the areas described in (3), the calculated depth of Moho is about 10 to 20 percent deeper than the depth given in (3).6) The “discontinuities” in the crust might not be so sharp as Moho discontinuity.

Geographical Distribution Patterns of Daily Snowfalls in Hokuriku (Japan Sea Side) Area

Japan Sea Side area is the snowiest region in the world. Geographical distribution maps of daily snowfall and those of the occurence of excess snowfall (mean snowfall + 2 standard deviation) of the area have been drawn for 98 days during two winters of 1955-57. And four typical distribution patterns were distinguished. Relations between these patterns and their respective synoptic charts and upper-air conditions were checked and the followings were resulted;1) Scattered Mountain-Snow Type (Fig. 2) …This pattern used to occur at the early stage of the monsoon burst and at the passing of the cold front. The amount of snowfall is not so deep and the areas of deeper than 20cm snowfalls are limited and scattered only on the mountaneous areas. The frequency of the occurence is more predominent than the other types and occupies about 30% of the snow days. The upper-air is relatively warmer (not colder than -18°C) on this occasion.2) Mountain-Snow Type (Fig. 3) …Heavy snow falls mainly on the central backbone mountain area of Japan. This pattern often happens at the strong monsoon bursts and lasts 1-2 days. Snowfall reaches frequently over 80cm and the excess snowfall covers more extensive areas than those of No. 1 type. Judging from the distribution pattern and others, this type of snowfall is typically orographic origin and is observed when the upper-air is colder than -18°C and the wind speed is faster than 18m/sec at 700mb level.3) Coastal-Snow Type (Fig. 4) …Heavier snow falls on the coastal plains or hilly inland areas than the mountaneous areas. The daily amounts are about 20-40cm. This pattern seems to appear accompanied by the active local front which is called as Hokuriku front when the pressure gradient over the Japan Sea is not steap and the monsoon is fairly weak. The average persistence of this pattern is 2-3 days. The typical upper-air condition is the weaker wind of less than 21m/sec.4) Heavy Snowfall Type (Fig. 5) …All over the area reports heavy excess snowfall and locally it reaches more than 100cm often. The pattern appears when the monsoon is moderately strong and the upper-air is colder than -20°C. We may subdivide this into the mountain-snow type heavy snowfall and the coastal-snow type heavy snowfall.The sequence of these patterns for the period are shown on Fig. 6.The figure 7 shows the topography of the Hokuriku area and the daily amounts of snowfalls during Feb. 11-15, 1957 at 4 different cross-sections from the sea to the mountain arranging from the east to the west. On Feb. 11 the mountain type heavy snow falls, 12th shows the mountain-snow type distribution and 13-15th are the coastal-snow type distributions.