Geology topics

S. Self

Publications and source records attributed to S. Self.

3 recordsLinked to original sources

USGS2009

Effects of megascale eruptions on Earth and Mars

Volcanic features are common on geologically active earthlike planets. Megascale or "super" eruptions involving >1000 Gt of magma have occurred on both Earth and Mars in the geologically recent past, introducing prodigious volumes of ash and volcanic gases into the atmosphere. Here we discuss felsic (explosive) and mafi c (flood lava) supereruptions and their potential atmospheric and environmental effects on both planets. On Earth, felsic supereruptions recur on average about every 100-200,000 years and our present knowledge of the 73.5 ka Toba eruption implies that such events can have the potential to be catastrophic to human civilization. A future eruption of this type may require an unprecedented response from humankind to assure the continuation of civilization as we know it. Mafi c supereruptions have resulted in atmospheric injection of volcanic gases (especially SO 2 ) and may have played a part in punctuating the history of life on Earth. The contrast between the more sustained effects of flood basalt eruptions (decades to centuries) and the near-instantaneous effects of large impacts (months to years) is worthy of more detailed study than has been completed to date. Products of mafi c supereruptions, signifi cantly larger than known from the geologic record on Earth, are well preserved on Mars. The volatile emissions from these eruptions most likely had global dispersal, but the effects may not have been outside what Mars endures even in the absence of volcanic eruptions. This is testament to the extreme variability of the current Martian atmosphere: situations that would be considered catastrophic on Earth are the norm on Mars. ?? 2009 The Geological Society of America.

Special Paper of the Geological Society of America↗

USGS1996

A new model for the emplacement of Columbia River basalts as large, inflated pahoehoe lava flow fields

Extensive flows of the Columbia River Basalt (CRB) Group in Washington, Oregon, and Idaho are dominantly inflated compound pahoehoe sheet lavas. Early studies recognized that CRB lavas are compound pahoehoe flows, with textures suggesting low flow velocities, but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks. However, small volume ( < 1 km3) compound pahoehoe flows on Kilauea, Hawai'i, demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger (10-20 km3) pahoehoe flows in Iceland. The vertical distribution of vesicles and other morphologic features within CRB lava flows indicate that they grew similarly by inflation. Small pahoehoe lobes at the base and top of many CRB pahoehoe lava flows indicate emplacement in a gradual, piecemeal manner rather than as a single flood. We propose that each thick CRB sheet flow was active for months to years and that each group of flows produced by a single eruption (a flow field) was emplaced slowly over many years. Copyright 1996 by the American Geophysical Union.

Geophysical Research Letters↗

USGS1987

Recent geologic history of lake Atitlán, a caldera lake in western Guatemala

Lake Atitlán, a caldera lake in western Guatemala, was investigated for evidence of recent volcanic and tectonic activity. No vents, faults, or folds are apparent on high-resolution seismic reflection profiles of lake sediment, representing at least 17,500 years and probably more than 35,000 years of deposition. Three post-caldera stratovolcanoes (San Pedro, Tolimán, and Atitlán) have grown in southern parts of the caldera and two deltas have grown from the north shore of the lake. Elsewhere, the caldera is occupied by Lake Atitlán, which is more than 300 m deep and has a relatively flat floor. Refraction profiles suggest that the original floor of the caldera lies ca. 300 m below the current lake floor, but prodigious amounts of methane gas in the lake sediment attenuated seismic signals and prevented any detailed view of the original caldera floor or faults along which the floor is presumed to have collapsed. Piston cores from deep basins of Lake Atitlán record ca. 2,000 years of unusually rapid sedimentation (ca. 0.5 cm/yr). Only one thin silicic ash layer was penetrated, and it is probably from a distant source. Cores contain evidence of Mayan disturbance of the environment around the lake and, to a lesser degree, of the lake itself; they might also record episodes of increased thermal activity, each lasting several decades. Heat-flow measurements inside and just outside the caldera are high (290 and 230 mW m −2 ), suggesting hydrothermal convection and a shallow heat source. High heat flow, a geological record of post-caldera silicic eruptions, and unexplained fluctuations of lake level (episodic tumescence ofthe lake floor?) suggest that magma remains beneath Lake Atitlán and that future eruptions are possible.

Journal of Volcanology and Geothermal Research↗