The 1998 eruption of Axial Seamount: New insights on submarine lava flow emplacement from high‐resolution mapping

Abstract

Axial Seamount, an active submarine volcano on the Juan de Fuca Ridge at 46°N, 130°W, erupted in January 1998 along 11 km of its upper south rift zone. We use ship‐based multibeam sonar, high‐resolution (1 m) bathymetry, sidescan sonar imagery, and submersible dive observations to map four separate 1998 lava flows that were fed from 11 eruptive fissures. These new mapping results give an eruption volume of 31 × 106 m3, 70% of which was in the northern‐most flow, 23% in the southern‐most flow, and 7% in two smaller flows in between. We introduce the concept of map‐scale submarine lava flow morphology (observed at a scale of hundreds of meters, as revealed by the high‐resolution bathymetry), and an interpretive model in which two map‐scale morphologies are produced by high effusion‐rate eruptions: “inflated lobate flows” are formed near eruptive vents, and where they drain downslope more than 0.5–1.0 km, they transition to “inflated pillow flows.” These two morphologies are observed on the 1998 lava flows at Axial. A third map‐scale flow morphology that was not produced during this eruption, “pillow mounds,” is formed by low effusion‐rate eruptions in which pillow lava piles up directly over the eruptive vents. Axial Seamount erupted again in April 2011 and there are remarkable similarities between the 1998 and 2011 eruptions, particularly the locations of eruptive vents and lava flow morphologies. Because the 2011 eruption reused most of the same eruptive fissures, 58% of the area of the 1998 lava flows is now covered by 2011 lava.

Three‐Dimensional Seismic Imaging of Ancient Submarine Lava Flows: An Example From the Southern Australian Margin

“…The forced folds are interpreted to have played an important role in governing the distribution of lava flows, as evidenced by the flows that pond within the paleo‐topography created by the forced folds. Many types of submarine lava flows have sheet‐like geometries (e.g., Chadwick et al, ) similar to the tabular flows in this study. Since we are unable to resolve the crustal features we are unable to determine whether the flows represent ropey, pillowed or jumbled flows (e.g., Gregg & Fink, ).…”

“…Flow morphology is controlled by lava rheology, effusion rate, cooling rate, lava viscosity, and the underlying slope (see Gregg & Smith, ; Griffiths & Fink, ; Hulme, ; also White et al, ). Observations from multibeam sonar, high‐resolution bathymetry, sidescan sonar imagery, and submersible dives reveal that these flows produce distinctive, mappable relief at the seafloor (e.g., Ballard & Moore, ; Ballard & van Andel, ; Chadwick et al, ; Fox et al, ). As well as forming a critical part of the Earths' cycle of crustal growth, submarine lava flows also play an important role in natural resource systems such as aquifers and petroleum systems (e.g., Millett et al, ; Watton et al, ).…”

“…The products of submarine volcanism are inherently more difficult to study than their subaerial counterparts. Remotely Operated Vehicles (ROV) and Autonomous Underwater vehicles (AUVs) are commonly used to gather data from inaccessible regions of the seabed (e.g., Chadwick et al, ; Mitchell et al, ). Studies using data sets collected by these methods are capable of observing meter‐scale features of lava flows, yet lack the ability to map volcanic provinces over tens of kilometers.…”

Emplacement of submarine lava flow fields: A geomorphological model from the Niños eruption at the Galápagos Spreading Center

“…Lava flows drained out to pillowed margins that are similar to the “inflated pillow flows” described at the JdF by Chadwick et al . []. As effusion rates waned, vent‐proximal lava morphology transitioned from lobates to pillows, building haystacks, larger clusters and ridges of pillow mounds that filled the original eruptive fissure.…”

“…Lava flow fields at intermediate‐spreading MORs bear many morphological similarities to lava flow fields at slow and fast spreading MORs, despite differences in scale. For example, the 1998 and 2011 eruptions at Axial Seamount on the JdF and several eruptions described herein at the GSC 92°W produced lava flow fields that are similar in appearance to those at the fast spreading EPR; however, those at the JdF are much larger (∼31 × 10 6 m 3 ) [ Chadwick et al ., ] and those at the GSC 92°W are much smaller (∼2 × 10 5 −12 × 10 6 m 3 ) [ Colman et al ., ] than the 2005–2006 northern EPR eruption (∼22 × 10 6 m 3 ) [ Soule et al ., ], and all of these eruptions are much smaller than the Aldo‐Kihi and Animal Farm lava flow fields (140 and 220 × 10 6 m 3 , respectively) [ Sinton et al ., ] at the superfast spreading southern EPR 17°S–19°S. Alternatively, the type of elongate, hummocky volcanic ridges that dominate at slow spreading MORs [e.g., Searle et al ., ] are also present at the GSC 92°W and 95°W [ Colman et al ., ] and at the Gorda and JdF ridges [ Yeo et al ., ], albeit on a smaller scale.…”