Chocolate tablet aspects of tectonics of Meshkenet Tessera on Venus

The intrablock deformation of Meshkenet Tessera on Venus is mostly due to responses of the uppermost surface bedrock to tensional stresses. It is found that complex deformation structures within the highland blocks resemble those of formed in chocolate tablet boudinaging which has taken place after original parallel faulting and bar-like crustal block formation. The high-angle tessera structures with varying cross-cutting relations define styles and locations of multiphase deformation most evidently related to local relaxation of tessera topography. Series of progressive or superposed fracturing events with alternating fault directions took place at high angles during this relaxational deformation. Compressional ridges often surround these tesserae.     

Ridge systems related to Martian impact craters

Wrinkle ridge systems within and around Martian highland craters were studied in order to find their basin-induced and regional aspects. Most prominent ridge directions indicate regional tectonic patterns. Radial ridges near large craters are often slightly deflected along regional or global ridge systems. Crater floor ridges have simpler local distributions. Smaller or older craters are less resistant against the effects of global or regional stress systems. In craters concentric ridge rings locate at 0.8 crater radius with additional minor rings at 0.66, 0.44 and 0.94 crater radius. This pattern illustrates compression of lava fill over buried topography.     

Ridge belt tectonics of Ganiki Planitia on Venus

The main major ridge belts of Ganiki Planitia on Venus (Lama, Ahsonnutli and Pandrosos Dorsa) are part of the fan-shaped ridge belt complex along the 200 parallel of longitude. These ridge belts with evidence of crustal shortening support the idea of a large-scale E-W compression. The ridge belt patterns indicate a N-S shear component. These forces are explained by a triangular planitia area which compressed by surrounding terrains. The crustal shortening and ridge belt formation indicates compressional plate movement stresses in the uppermost lithosphere.Three sizes of ridge belt structure are to be found within Ganiki Planitia. (1) The ridge belt spacing of 200–400 km can be used to estimate the depth of the major uppermost homogeneous layer of Venus. There are numerous volcanic coronae, paterae and montes located along the main ridge belts or at their junctions. (2) Mid-size ridge groups or subbelts are to be found within the major ridge belts. These are formed by more local responses to tectonic stresses in the stratified uppermost crust. A wavelength of 40–70 km can be seen as a result of bending of the crustal strata and may relate to its thickness. (3) Small individual ridges are connected with most local stresses, defining places where the surface layers broke along the crests of large ridge belts or mid-scale subbelts. Radial and concentric mare ridge-like structures around coronae indicate that corona formation was effective at a sufficiently close vicinity to fault the surface.     

Public participation in monitoring programmes as a tool for lakeshore monitoring: the example of Lake Pyhäjärvi, Karelia, Eastern Finland

Lake Pyhäjärvi, on the border between Finland and Russia in Karelia, is a very valuable clear-water lake of the Lobelia type. It belongs to the European Union's Natura 2000 programme in Finland, and has been included in regional and national monitoring programmes since the 1960s. The main monitoring station is situated near the outlet of the lake. Deterioration of its water quality was suspected already in the 1980s because of decreasing Secchi depths (transparency) and increasing chlorophyll a.The occurrence of algal blooms on the lakeshores is monitored weekly during each summer at one site on Lake Pyhäjärvi (site 1). This is a part of nationwide intensive algae monitoring programme organised by the environmental authorities together with voluntary observers at some 270 lake sites in Finland since 1998. Since 1997, Secchi depth observations have been carried out by volunteers biweekly or monthly at 17 sites on the lake. In the vicinity of one of these transparency observation sites (station 100), intensive monitoring of algae has been carried out. At this lakeshore monitoring site 69 algal observations were made, ten of which recorded algal blooms during the study period 1998–2002. The observed algal blooms were caused by algae of the Anabaena species, mainly by Anabaena lemmermannii. At Lake Pyhäjärvi the number of algal bloom observations received from the public have decreased from the 1990s to the 2000s. The range of Secchi disc transparency was 5.0–8.4 m with a mean value of 6.2 m at station 100 and 4.3–7.7 m (mean 6.1 m) at the main monitoring station 2 during the open water periods in 1998–2002. During this study period, the maximum values at site 100 seem to have increased slightly, which might indicate some improvement in the water quality due to decreased point source loading.We conclude that the intensive algal monitoring results of 5 years at the lakeshore site and the transparency results — both compiled by trained volunteers — reflect an improvement in the state of Lake Pyhäjärvi in Karelia. This conclusion is in accordance with the long-term water quality and short-core studies of sedimentary diatoms in Lake Pyhäjärvi. We suggest that the intensive algal observations and transparency measurements are both suitable methods for the monitoring of lakeshores and lakes, and that both are suitable for voluntary monitoring. We found public participation a good tool for monitoring lakes and lakeshores.     

Composite graben tectonics of Alba Patera on Mars

The Alba Patera main graben zone is radial to the Tharsis bulge, indicating the importance of the Tharsis bulge-related peripheral rift tectonics. The concentric grabens around the Alba Patera area are also partly caused by crustal bending due to the central load of the Alba Patera volcano. These two graben sets partly coincide forming composite structures. Both tectonic systems were still active after the last major volcanic lava extrusions took place. After this, the crater chain grabens, radial to the northernmost part of the Tharsis bulge were formed. These collapse craters were evidently caused by the late-tectonic forces due to the northern Tharsis and adjoining lava loads, resulting in flexural tension and activating previous faults.     

Venusian novae (Astra): Classification and associations to different geological environments

On the Venusian surface, there can be found a rather large population of structures with prominent radial features. The term “nova” or “astrum/astra” are used to describe this special group of volcanotectonic structures with a stellate fracture pattern radiating around a central summit or fracture. In this paper, we studied the distribution and characteristics of 74 novae to determine if there are suitable ways to categorize them and to find out how this categorization could explain the differences in nova characteristics. The nova locations establish that these structures are not distributed sporadically, but they display both latitudinal and longitudinal concentrations. In addition, it is evident that the geological environments represent the major differences between individual novae. Most of them, in general, are connected to some larger volcanotectonic unit. The differences in geological surroundings can be used as the basis for characterizing novae by dividing them into different categories: (a) novae located either within or close to a rather large deformation zone, (b) novae located on plains, (c) novae located close to tessera terrain, and (d) novae situated within volcanic areas either close to volcanoes or within an area with a high density of coronae. The analysis of this characterization establishes that geological environments are the main cause for divergent nova characteristics, i.e., differences in morphology, volcanism, and topography, which, on the other hand, are possible ways to classify novae. In particular, the morphological classification (Type I, novae with features radiating from the same point; Type II, radial structures radiating from a fissure or other linear structure; Type III, lava flows or fields covering radiant point area; Type IV, semiradial structures which do not radiate from a well-defined radiant point, fissure, or area) shows some correlations between geological environments and the type of nova, indicating that the morphological appearance and the location—and, thereby, the geologic environment—of the novae are correlated to some extent.     

On the air‐sea interaction in areas of thermal marine fronts in the Greenland Sea

Abstract

The effects of marine fronts on the local atmospheric surface layer and air‐sea interaction were studied. Several mesoscale fronts were crossed by a research vessel in the Greenland Sea. Air temperature, humidity and stability conditions, and the fluxes of momentum, as well as sensible and latent heat, were investigated. For relatively calm conditions, close air‐sea coupling was observed in the temperature whereas for stronger winds, the air temperature of the surface layer was not markedly modified by the front below. Changes in the moisture content in the frontal area were observed and, in one case, evaporation was observed on the warm water side and condensation on the cold water side of the front. Frontal differences in heating from the sea were assumed to affect the surface‐layer wind field.     

Fractal properties of crater ejecta outlines on Venus

Fractal property or self-similarity exists abundantly in many aspects in our universe. Fractals are rich in geology and have certain relations to various geological processes. This article presents analyses of fractal properties of 18 impact crater ejecta margins on the surface of Venus. The structured walk method was used to measure the length of perimeter of the ejecta margin and the resulting Richardson plots were investigated. EveryR-plot has a first linear part, a second part and a main scattering part. The variations seen in the second part include information on the formation and geology of the crater ejectas. The fractal dimension of the second part is related to the perimeter of the ejecta and thus to the impact energy. The ratio of the square of the perimeter to the area describes the lobateness of the ejecta and has a positive correlation to the perimeter in a way similar to that between the fractal dimension of the second part and the perimeter. Two linear subparts in the second part indicate different fractal properties due to various processes dominating on different scales. Scattering in the middle of the second part indicates the scale and type of the ejecta lobes. The smooth scattering over the entire second part is related to impact angle and energy. A threshold value beyond which the structured walk method cannot be used was observed at a ruler length of about 1/10 of the perimeter.     

Mapping previously unmapped planetary surface: A supervised multispectral terrestrial/aquatic approach in northeastern Finland

Although large numbers of imageries over planetary surfaces have been aquired by notable space missions over the past twenty years, the versatile technical remote sensing achievements, which have found their long-term and successful applications within the fields of different geosciences, have not been employed in planetology. High resolution imageries allow small-scale surface features to be observed, various filters allow different wavelength bands and surface units of different colour or spectral reflectance to be recorded. Also long-term missions transmit information about multitemporal changes, but such diversified multitemporal surface mapping, as possible by Landsat MSS data, to say nothing of the potential of the Landsat TM and SPOT equipment, are mostly unexecuted.This paper contains an example of the aquatic environment research by computer-assited remote sensing using Landsat MSS data. The western parts of Lake Yli-Kitka, northeastern Finland were studied and mapped according to spectrally identified classes which were improved after field work by associated reclassification.The Landsat classification of open water areas depends on the water quality and depth, or shore distance relations. The recognition of aquatic vegetation complexes is based on the main life-form (helophytic, nymphaeid, isoetid etc.) and the amount of recorded radiation reflected from the chlorophyll (or from other shallow bottom coverage) in respect to the open water surface radiation absorbance within near infrared wavelengths.Aquatic areas are quite featureless in respect to their reflectance, especially in northeastern Finland area studied. The use of wide-channel multispectral satellite data has demonstrated to be valid under quite difficult circumstances. Similar or preferably more up-to-date planetary imagery data could be of high utility value in mapping various surface units of the terrestrial planets and large moons.     

Magma chamber -related development of Alba Patera on Mars

The formation of the central calderas of the Alba Patera summit area is proposed to have been caused by collapse(s) into relatively shallow and wide magma chamber(s). The subduction or collapse of the whole central Alba Patera area and the formation of peripheral circular fossae grabens around it were caused by a deeper, wider and more primary magmatic process which was more directly connected to the ascending hot mantle.