Lava flows on Mars: Analysis of small surface features and comparisons with terrestrial analogs

Abstract

Small‐scale surface features on lava flows provide information on the eruption parameters and the volcanic history of the flows in which they occur. High‐resolution images of four sites on Mars reveal lava flows with a different type or combination of features including pressure ridges, tumuli, festoon ridges, and ring ridges. Pressure ridges, tumuli, and pressure plateaus are spaced irregularly and tend to be oriented parallel to flow. They are formed by inflation of small flow lobes and are indicative of compound flows emplaced by sporadic eruptions with low effusion rates. Festoon ridges are oriented transverse to flow direction, mimic the flow margin, and have a regular spacing. Using a model by Fink and Fletcher (1978) and Fink (1980 a) interior viscosity values of approximately 108 Pa s were calculated for festoon ridges tens to hundreds of meters apart and a few meters high on two basalt flows in Iceland and a flow on Mars. This viscosity is comparable to results from similar studies of more silicic flows and suggests that high viscosities are necessary to form large festoon ridges. By analogy to the Icelandic flows, Martian flows containing festoon ridges are considered to be large, single unit basalt flows emplaced through flood‐style eruptions. High viscosity of the basaltic flows may result from cooling, a high crystal content, or low effusion temperatures. Disruption of the surface of some of these large sheet flows possibly by lava‐water interaction is suggested by the presence of ring ridges and rugged terrain consisting of mesa‐like mounds and channel‐like troughs.

Bell Regio, Venus: Integration of remote sensing data and terrestrial analogs for geologic analysis

“…The portions which show thiough aie quite rough at scales of several hundred meters, with structures that are knobby in some locales and ridge-like in others. This relatively old unit may have formed by eruption of highly viscous magma, similar to the festooned flow studied by Moore et al [1992], or by slow inflation of a tumuli field by more ordinary basaltic magma [Theilig and Greeley, 1986]. The association of such a flow, the steep edifice, and the adjacent dome offers a view of several features which are uncommon on Venus.…”

The initial cooling of pahoehoe flow lobes

“…It has also been argued that continental flood basalt flow units are inflated pahoehoe sheet flows (e.g., Hon and Kauahikaua 1991;Self et al 1991). Pahoehoe flows may also have been detected on Mars (Theilig and Greeley 1986) and Venus (Bruno et al 1992). In Hawai'i, pahoehoe flows cover approximately 86% of Kilauea Volcano (Holcomb 1987) and 50% of Mauna Loa (Lockwood and Lipman 1987).…”

Thick lava flows of Karisimbi Volcano, Rwanda: insights from SIR-C interferometric topography

“…If these morphologic data are combined with field observations, reasonable estimates of yield strength and viscosity can be made, in some cases allowing estimates of effusion rate (de Silva et al 1994) and other eruptive parameters. Equally exciting are the possibilities for comparative and planetary volcanology (Theilig and Greeley 1986) that will arise when highquality DEMs become more widely available from instruments such as the Mars Orbiter Laser Altimeter. Just as volcano morphology holds clues to the evolution of individual volcanoes, comparative morphology holds the promise of new insights into lava flow behavior, vent locations, and the interaction of tectonic and volcanic events through detailed mapping of areas such as Nyiragongo, Erta Ale, and other rift zone volcanoes.…”