INFLATED SHEET FLOWS AND THE OCCURRENCE OF BULBOUS SQUEEZE-UPS

• Main Author: Olson, Grady D
• Format: Text
• Language: unknown
• Published: DigitalCommons@Macalester College 2016
• Subjects: Iceland; Krafla; Lava; Bulbous Squeeze-up; Geochemistry; PCA; Earth Sciences; Geology
• Online Access: https://digitalcommons.macalester.edu/geology_honors/20; https://digitalcommons.macalester.edu/cgi/viewcontent.cgi?article=1022&context=geology_honors

In the far north of Iceland, the nine Krafla Fires of 1975 to 1984 produced large volumes of basaltic lava primarily by fissure fed eruptions, which created a variety of volcanic features. Bulbous squeeze-ups, an unusual and previously undescribed lava flow feature, were discovered during a 2015 field study of an inflated flow field formed during the September 1984 eruption at Krafla. Field studies indicate bulbous squeeze-ups form only on linear pull-apart features, and are likely of high viscosity upon extrusion. The jumbled nature of the flow field surrounding these bulbous squeeze-ups suggests a pulsed, somewhat violent, and rapid emplacement and cooling history. Geochemical and petrographic investigations indicate that bulbous squeeze-ups, elongate squeeze-ups, and pahoehoe plates from the northern flow field are texturally and chemically indistinguishable (e.g., Cohen’s d < 2 for whole rock major and trace element comparisons) suggesting that these features formed from a single, homogenous and unfractionated magma. Principal component analysis (PCA) of major and trace element concentrations further supports this interpretation. The lack of literature describing similar squeeze-up morphologies suggest that the factors that controlled the formation of bulbous squeeze-ups in the northern flow field are somewhat unique to Krafla. Specifically, the formation of bulbous squeeze-ups are largely controlled by pulsed inflation, low slope, high effusion rate, and high viscosity upon extrusion. Importantly, if the manner in which bulbous squeeze-ups form is determined, the identification of this distinctive morphology could be telling of conditions of past eruptions on earth, as well as on other planets with observable lava flows.