Structural deformation and sedimentation in an active Caldera, Rabaul, Papua New Guinea

H. Gary Greene; D. L. Tiffin; C.O. McKee

Home/Archive/USGS

USGS · 70014467

Structural deformation and sedimentation in an active Caldera, Rabaul, Papua New Guinea

H. Gary Greene·D. L. Tiffin·C.O. McKee

View original source ↗Export metadata ↓

Abstract

Recent seismic and tectonic activity in Rabaul Caldera, Papua New Guinea, suggests that magma is accumulating at a shallow depth beneath this partially submerged structure and that a new volcano may be developing. Changes in onshore elevation since 1971 (as much as 2 m on south Matupit Island) indicate that rapid and large-scale uplifts have occurred on the seafloor near the center of the caldera. The frequency of seismic events within the caldera has also increased during this period. Earthquake locations define an elliptical ring surrounding the center of this uplift within the caldera. A marine geophysical survey in 1982 by the U.S. Geological Survey's R/V "S.P. Lee" in Rabaul Caldera shows the development of a bulge in the seafloor near the center of the caldera. High-resolution seismic reflection profiles show that this bulge consists of two domal uplifts bounded and separated by two major north-south-trending fault zones. Deformed sediments overlie these zones; a prominent slump flanks the area of the bulge. Five major acoustic units were identified in the seismic reflection profiles: an acoustic basement and four sedimentary units consisting of irregularly layered, cross-layered, contorted, and well-layered sequences. The acoustic basement is probably composed of crystalline volcanic rocks, and the layered acoustic units are probably sediments, primarily ash deposited in different environments. The cross-layered, irregularly layered, and contorted units appear to have been deposited in a dynamic environment subjected to strong currents, seismicity, and/or mass wasting, while the well-layered units were deposited in a low-energy environment. Locally, well-layered sequences interfinger with the other sedimentary units, indicating a transitional environment that alternated between high-energy and low-energy depositional processes. A submarine channel cuts most of the acoustic units and appears to be the conduit for sediment transport out of the caldera; it occupies an older buried channel north of the caldera that is presently being exhumed. In the south, active erosion of well-layered sediments is taking place. What are believed to be several young volcanic cones also disrupt the depositional layers. We conclude that the bulge in the seafloor and the associated fault zones are a result of emplacement of magma at a shallow depth. Contorted sediment and slumps adjacent to the bulge are probably the result of uplift and seismic activity. The pattern of seismicity appears to reflect increased magma pressure at depth beneath the caldera floor. This activity may eventually lead to an eruption. ?? 1986.

Explore related subjects

Journal of Volcanology and Geothermal Research Article

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

H. Gary Greene, D. L. Tiffin, C.O. McKee. 1986. Structural deformation and sedimentation in an active Caldera, Rabaul, Papua New Guinea. https://pubs.usgs.gov/publication/70014467

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Tree-ring isotope and satellite records of vegetation changes reveal transition from cold to hot degassing in the Yellowstone Plateau volcanic field

Magmatic degassing often provides the earliest clues to changes in magmatic systems, yet detection and characterization of the escaping gases is challenging. Recent work suggests that satellite-based normalized difference vegetation index (NDVI) calculations may provide an indirect method for detecting changes in degassing. Here, we use tree ring δ 13 ⁢C , δ 18 ⁢O , and radiocarbon ( 14 C) data to assess NDVI as a proxy for diffuse magmatic degassing and to better understand the development of the Tern Lake thermal area (TLTA) in the Yellowstone Plateau volcanic field, USA. We measured δ 13 ⁢C , δ 18⁢ O , and 14 C in wood from four TLTA trees and two control trees. The 14 C data indicate that TLTA trees were exposed to significant magmatic CO 2 degassing during the 1990s, corroborating satellite-based NDVI changes observed at a time when no other indications of degassing existed. Magmatic degassing also increased water availability for trees closest to the degassing center, as indicated by decreasing δ 13 ⁢C and δ 18⁢ O values relative to background throughout the 1980s and 1990s. Increased H 2 S degassing in the early 2000s impaired stomatal functioning, increasing δ 13 ⁢C and δ 18⁢ O values. These isotope values were strongly correlated with NDVI, demonstrating that ground- and satellite-based approaches yield similar conclusions. Together, the satellite and isotope datasets suggest that TLTA degassing was characterized by cold CO 2 emissions with minimal H 2 S until the early 2000s, when it transitioned to a high-temperature system with significant CO 2 and H 2 S emissions. These results add to a growing body of evidence that vegetation responses can be an effective proxy for magmatic degassing.

Wyoming↗

USGS2026

Dynamics and evolution of the Kı̄lauea lower East Rift Zone 2018 fissure 8 lava flow and implications for multiphase magma properties

The 2018 Kı̄lauea lower East Rift Zone (KLERZ) eruption was one of the most voluminous eruptions on the Island of Hawai’i in the past 200 years, leading to major disruption and destroying over 700 homes and structures. The majority of the erupted magma was emitted as a lava flow from Ahu’ailā’au (fissure 8), which was active from late May to early August. To better understand the evolution of long-lived channelized lava flows, we examined the evolution of velocity, texture, and inferred rheology of the fissure 8 lava in space and time. We quantified lava flow surface velocities using particle image velocimetry in more than 200 aerial videos that span the lava flow duration and length. Velocity measurements were analyzed together with vesicularity and crystallinity measurements from 9 co-located post-eruptive field samples to understand the textural evolution of this flow and its impact on lava rheology and flow velocity. The fissure 8 flow was highly vesicular, with 79%–88% vesicularity at the vent, decreasing to 16%–26% vesicularity 12.5 km from the vent. The volume fraction occupied by crystals 50 in size increased from 6% at the vent to about 18% at 12.5 km downstream. We find that the effective flow viscosity increased at a quadratic rate with distance. Using experimentally determined liquid viscosity and applying established models to account for the effect of crystals and bubbles, we attribute this increase primarily to textural evolution driven initially by the near-vent loss of deformable bubbles and later by cooling and crystal growth. We demonstrate the importance of accounting for the evolution of vesicularity and the role of vesicles by showing that utilizing this capability in the open-source thermo-rheological lava flow propagation model PyFLOWGO allows for more accurate predictions of the observed flow velocities. Our modeling results suggest that small bubbles behaving rigidly are required to simulate the observed flow length, speed, and viscosities. Flow velocities of the fissure 8 lava also varied with time, driven by near-daily collapse events of the summit caldera. Temporal velocity changes were characterized by a period of steep acceleration, with the volumetric flux peaking around 4 h after a caldera collapse, followed by a period of gradual deceleration lasting up to 40 h or until the next collapse event. We use this temporal behavior to estimate the compressibility of the magma inside the plumbing system between the summit reservoir and the lower East Rift Zone. Overall, quantifying the spatial and temporal evolution of the KLERZ eruption provides information about magma and lava properties that can inform predictive modeling and hazard assessment during an eruption.

Hawaii↗

USGS2026

Small-volume tephra deposits of the May 1924 explosions from Halemaʻumaʻu, Kīlauea volcano, and their origin

More than 50 explosive eruptions occurred from Halemaʻumaʻu at Kīlauea volcano over 17 days from May 11 to 27, 1924. Ballistics weighing as much as 14,000 kg were ejected and most landed within 2 km of the vent. Fine ash made up a major component of the tephra and was dispersed tens of kilometers downwind. Draining of the Halemaʻumaʻu lava lake occurred in late February 1924, with the crater floor eventually subsiding by a further ∼70 m (to ∼180 m below the crater rim) by the time the first explosions took place during the night of May 10–11. The largest explosions occurred on May 17–18 and smaller explosions continued until May 27, at which point Halemaʻumaʻu had more than doubled in width and depth. The explosions generated plumes reaching up to ∼10 km high with ballistics ejected up to 2 km from the crater. Almost 100 years later, we investigate and characterize the preserved tephra deposits within ∼3 km of the 1924 crater rim. Grain size and shape analyses were performed on 202 samples collected from 34 tephra profiles using dynamic image analysis, with a subset of layers from nine tephra profiles used for componentry (200 grains per layer in the 0.5–1 mm size fraction). Additionally, we characterize the average diameters (using the five largest clasts) at 216 locations and measure the average diameters of 2291 ballistics (largest per ∼100 m 2 area). Physical descriptions from fieldwork and grain size distributions were used to subdivide the tephra layers into five lithofacies: coarse homogeneous, fine homogenous, red ash, accretionary lapilli-bearing, and finely laminated. Grain size versus shape data show a range of values that demonstrate most grains are dense, smooth, and equant, in alignment with lithic clasts dominating the tephra componentry. The fine grained and accretionary lapilli-bearing nature of some of these lithofacies confirms that water influenced the style of the explosions. However, we also note juvenile clasts within many of the tephra layers, indicating that many of the layers were formed during phreatomagmatic explosions (sensu stricto), despite the eruptive mechanism being dominantly phreatic. Juvenile clasts are more abundant higher in the tephra profiles, suggesting that juvenile magma was more involved later in the explosive sequence. Thermal and hydrologic modeling indicate that groundwater inflow into a short-lived, small-diameter volcanic conduit (10-m to 120-m-diameter used for modeling) during the 78–85 days preceding the first explosion provides a physically plausible mechanism for this eruptive sequence.

Hawaii↗