Search

A typographical error contained in Quick et al. (2016) indicates the incorrect units for the value of the combined quantity (roh(exp. 3)o) that is the basis of Figs. 5, 6, and 7, and Tables 2 and 3. Using the values of ro and ho provided in Table 2, it can easily be shown that the combined quantity is correctly stated as roh(exp. 3)o =0.617 km(exp. 4). As correctly stated in Quick et al. (2016), the combined quantity of (roh(exp. 3)o) determines the family of curves shown in Fig. 5. The derivation of this relationship is shown below for completeness. Note that all results as reported in Quick et al. (2016) remained unchanged.

Explosive volcanic eruptions can produce sustained, buoyant columns of ash and gas in the atmosphere (Fig. 1). Large flood basalt eruptions may also include significant explosive phases that generate eruption columns. Such eruptions can transport volcanic volatiles to great heights in the atmosphere. Volcanic eruption columns can also redistribute chemical species within the atmosphere by entraining ambient atmosphere at low altitudes and releasing those species at much higher altitudes.

One key to understanding the history of resurfacing on Venus is better constraints on the emplacement timescales for the range of volcanic features visible on the surface. A figure shows a Magellan radar image and topography for a putative lava dome on Venus. 175 such domes have been identified with diameters ranging from 19 - 94 km, and estimated thicknesses as great as 4 km. These domes are thought to be volcanic in origin and to have formed by the flow of viscous fluid (i.e., lava) on the surface.

The Guinevere Planitia quadrangle of Venus (0-25degN, 300-330deg) covers a lowland region east of Beta Regio and west of Eistla Regio, including parts of Guinevere and Undine Planitiae. The V-30 quadrangle is dominated by low-lying plains interpreted to be of volcanic origin and exhibiting numerous wrinkle ridges. Using Pioneer Venus, Goldstone, and Arecibo data, previous investigators have described radar bright, dark, and mottled plains units in the Guinevere Planitia region, as well as arcuate fracture zones and lineament belt segments that define the Beta-Eistla deformation zone [1-5]. Magellan SAR images show that volcanic landforms compose the majority of the surface units in V-30 [6-7]. The quadrangle contains parts of four major volcanoes: Atanua (9degN, 307deg), Rhpisunt (3degN, 302deg), Tuli (13degN, 314deg), and Var (3degN, 316deg) Montes, and three coronae: Hulda (12degN, 308deg), Madderakka (9degN, 316deg), and Poloznitsa (1degN, 303deg). Seymour crater, located at 18degN, 327deg, is associated with extensive crater outflow deposits.

Figure 1 shows a radar image and topography for flat-topped, steep-sided "pancake" domes on Venus. At least 145 such domes have been identified on Venus [I] and are thought to be volcanic in origin [2]. Based on analysis of the dome surfaces, [3] suggested that only the late stage surface fractures are preserved, indicating entrainment and annealing of fractures during emplacement, consistent with a basaltic composition. Figure 1 shows a radar image and topography for flat-topped, steep-sided "pancake" domes on Venus. At least 145 such domes have been identified on Venus [I] and are thought to be volcanic in origin [2]. Based on analysis of the dome surfaces, [3] suggested that only the late stage surface fractures are preserved, indicating entrainment and annealing of fractures during emplacement, consistent with a basaltic composition.

Proxemy Research had a grant from NASA to perform science research on upwelling and volcanism on Venus. This was a 3 year Planetary Geology and Geophysics grant to E. Stofan, entitled Coronae and Large volcanoes on Venus. This grant closes on 12/31/05. Here we summarize the scientific progress and accomplishments of this grant. Scientific publications and abstracts of presentations are indicated in the final section. This was a very productive grant and the progress that was made is summarized. Attention is drawn to the publications and abstracts published in each year. The proposal consisted of two tasks, one examining coronae and one studying large volcanoes. The corona task (Task 1) consisted of three parts: 1) a statistical study of the updated corona population, with Sue Smrekar, Lori Glaze, Paula Martin and Steve Baloga; 2) geologic analysis of several specific groups of coronae, with Sue Smrekar and others; and 3) determining the histories and significance of a number of coronae with extreme amounts of volcanism, with Sue Smrekar. Task 2, studies of large volcanoes, consisted of two subtasks. In the first, we studied the geologic history of several volcanoes, with John Guest, Peter Grindrod, Antony Brian and Steve Anderson. In the second subtask, I analyzed a number of Venusian volcanoes with evidence of summit diking along with Peter Grindrod and Francis Nimmo.

Titan is a planet-size (diameter of 5,150 km) satellite of Saturn that is currently being investigated by the Cassini spacecraft. Thus far only one flyby (Oct. 26, 2004; Ta) has occurred when radar images were obtained. In February, 2005, and approximately 20 more times in the next four years, additional radar swaths will be acquired. Each full swath images about 1% of Titan s surface at 13.78 GHz (Ku-band) with a maximum resolution of 400 m. The Ta radar pass [1] demonstrated that Titan has a solid surface with multiple types of landforms. However, there is no compelling detection of impact craters in this first radar swath. Dione, Tethys and other satellites of Saturn are intensely cratered, there is no way that Titan could have escaped a similar impact cratering past; thus there must be ongoing dynamic surface processes that erase impact craters (and other landforms) on Titan. The surface of Titan must be very young and the resurfacing rate must be significantly higher than the impact cratering rate.

Proxemy Research had a grant from NASA to perform science research of upwelling and volcanism on Venus. This was a 5 year Presidential Early Career Award to E. Stofan, entitled "Upwelling and volcanism: Constraints from regional studies and geologic mapping." Here we summarize the scientific progress and accomplishments of this grant. Scientific publications and abstracts of presentations are indicated in the final section. This was a very productive grant and the progress that was made is summarized. Attention is drawn to the publications, abstracts, and talks given in each year. Volcanism and tectonism are the dominant geological processes that have shaped the surface of Venus, as revealed by the Magellan data. However, the development of a global geologic history for Venus has caused considerable debate (e.g., Head and Basilevsky, 1996; Guest and Stofan, 1999). The lack of global time horizons on Venus, such as that provided by impact craters on most bodies and the fossil record on Earth, make developing global stratigraphies for Venus difficult, if not impossible, with current datasets. Before the geologic history of Venus can be determined and used as a constraint on potential lithospheric thickness variations through time, it is necessary to perform detailed stratigraphic studies on a local to regional scale. In addition, detailed studies of specific types of venusian features and terrains, such as coronae, volcanic rises, and large lava flow fields, may help to constrain the lithospheric thickness and its potential variations in time and space. This report describes progress made during the five year award under a Presidential Early Career Award for Scientists and Engineers which allows researchers freedom to explore new areas of research.

Parga Chasma is a 10,000 km long fracture and trough system in the southern hemisphere of Venus. We analyze 128 coronae in the Parga region, including coronae along the chasma and those up to 900 km from the rifts.

Coronae are volcanotectonic features that are unique to Venus and are interpreted to be small-scale upwellings. A model in which upwelling causes delamination at the edge of the plume head, along with deformation of a pre-existing depleted mantel Layer, can produce the full range of topographic forms of coronae. If half of the coronae are active, delamination of the lower lithosphere could account for about 10% of venus's heat loss, with another 15% due to upwelling. Delamination may occur in other geologic enviroment and could help account for 'Venus' heat loss 'deficit'.

Large volcanic rises on Venus have been interpreted as hotspots, or the surface manifestation of mantle upwelling, on the basis of their broad topographic rises, abundant volcanism, and large positive gravity anomalies. Hotspots offer an important opportunity to study the behavior of the lithosphere in response to mantle forces. In addition to the four previously known hotspots, Atla, Bell, Beta, and western Eistla Regiones, five new probable hotspots, Dione, central Eistla, eastern Eistla, Imdr, and Themis, have been identified in the Magellan radar, gravity and topography data. These nine regions exhibit a wider range of volcano-tectonic characteristics than previously recognized for venusian hotspots, and have been classified as rift-dominated (Atla, Beta), coronae-dominated (central and eastern Eistla, Themis), or volcano-dominated (Bell, Dione, western Eistla, Imdr). The apparent depths of compensation for these regions ranges from 65 to 260 km. New estimates of the elastic thickness, using the 90 deg and order spherical harmonic field, are 15-40 km at Bell Regio, and 25 km at western Eistla Regio. Phillips et al. find a value of 30 km at Atla Regio. Numerous models of lithospheric and mantle behavior have been proposed to interpret the gravity and topography signature of the hotspots, with most studies focusing on Atla or Beta Regiones. Convective models with Earth-like parameters result in estimates of the thickness of the thermal lithosphere of approximately 100 km. Models of stagnant lid convection or thermal thinning infer the thickness of the thermal lithosphere to be 300 km or more. Without additional constraints, any of the model fits are equally valid. The thinner thermal lithosphere estimates are most consistent with the volcanic and tectonic characteristics of the hotspots. Estimates of the thermal gradient based on estimates of the elastic thickness also support a relatively thin lithosphere (Phillips et al.). The advantage of larger estimates of the thermal lithospheric thickness is that they provide an explanation for the apparently modest levels of geologic activity on Venus over the last half billion years.

UNKNOWN

UNKNOWN