Geology topics

Erik Sturkell

Publications and source records attributed to Erik Sturkell.

3 recordsLinked to original sources

USGS2016

Dimmuborgir: a rootless shield complex in northern Iceland

The origin of Dimmuborgir, a shield-like volcanic structure within the Younger Laxá lava flow field near Lake Mývatn, in northern Iceland, has long been questioned. New airborne laser mapping (light detection and ranging (LiDAR)), combined with ground-penetrating radar results and a detailed field study, suggests that Dimmuborgir is a complex of at least two overlapping rootless shields fed by lava erupting from the nearby Lúdentarborgir crater row. This model builds upon previous explanations for the formation of Dimmuborgir and is consistent with observations of rootless shield development at Kīlauea Volcano, Hawaii. The larger rootless shields at Dimmuborgir, 1–1.5 km in diameter, elliptical in plan view, &sim;30 m in height, and each with a 500-m-wide summit depression, were capable of storing as much as 2–3 × 10 6 m 3 of lava. They were fed by lava which descended 30–60 m in lava tubes along a distance of 3 km from the crater row. The height difference generated pressure sufficient to build rootless shields at Dimmuborgir in a timescale of weeks. The main summit depressions, inferred to be drained lava ponds, could have emptied via a 30-m-wide × 5-m-deep channel, with estimated effusion rates of 0.7–7 m 3 s −1 and minimum flow durations of 5–50 days. We argue that the pillars for which Dimmuborgir is famed are remnants of lava pond rims, at various stages of disintegration that formed during pond drainage.

Bulletin of Volcanology↗

USGS2009

Comparison of clast frequency and size in the resurge deposits at the Chesapeake Bay impact structure (Eyreville A and Langley cores): Clues to the resurge process

Collapse and inward slumping of unconsolidated sedimentary strata expanded the Chesapeake Bay impact structure far beyond its central basement crater. During crater collapse, sediment-loaded water surged back to fill the crater. Here, we analyze clast frequency and granulometry of these resurge deposits in one core hole from the outermost part of the collapsed zone (i.e., Langley) as well as a core hole from the moat of the basement crater (i.e., Eyreville A). Comparisons of clast provenance and flow dynamics show that at both locations, there is a clear change in clast frequency and size between a lower unit, which we interpret to be dominated by slumped material, and an upper, water-transported unit, i.e., resurge deposit. The contribution of material to the resurge deposit was primarily controlled by stripping and erosion. This includes entrainment of fallback ejecta and sediments eroded from the surrounding seafloor, found to be dominant at Langley, and slumped material that covered the annular trough and basement crater, found to be dominant at Eyreville. Eyreville shows a higher content of crystalline clasts than Langley. There is equivocal evidence for an anti-resurge from a collapsing central water plume or, alternatively, a second resurge pulse, as well as a transition into oscillating resurge. The resurge material shows more of a debris-flow-like transport compared to resurge deposits at some other marine target craters, where the ratio of sediment to water has been relatively low. This result is likely a consequence of the combination of easily disaggregated host sediments and a relatively shallow target water depth.

Chesapeake Bay↗

USGS2009

Precision leveling and geodetic GPS observations performed on Surtsey between 1967 and 2002

The load on the crust from the ~ 0.8 km 3 of eruptive products of the Surtsey eruption is expected to lead to subsidence of the Surtsey island by sagging of the lithosphere, compaction of material, and slumping of the volcanic edifice. Immediately after the eruption ended in the summer of 1967 a levelling line was established across the island to monitor this expected subsidence. The line originally contained 42 benchmarks. As Surtsey is subjected to extensive erosion, in particular in the western and southern parts of the island, the western section of the line has been lost to the sea. In the year 2002 the line ended with benchmark 28. Additional benchmarks were installed 1979, 1982, 1985 and 2002, to fill in gaps in the original line and another profile was installed through the Surtur I crater. Between 1967 and 2002 levelling has been performed eleven times. One benchmark was surveyed with geodetic GPS in 1992. The benchmark was resurveyed in 2000 and 2002 and the GPS network has been extended to comprise four points. In this report we have compiled the levelling data collected on Surtsey so far. Furthermore we present coordinates for the GPS-benchmarks. Continuing subsidence of Surtsey is observed with a decaying rate. The area around the Surtur I crater is the most stable part with a subsidence rate of 0.7 cm/yr in the period 1991–2002. The largest subsidence is observed at the flanks of the island with rates up to 1.4 cm/yr. The excess rate here is most likely caused by slumping of the sides of the island.

Surtsey↗