IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

0P2_3D-O10

Room B1

Date/Time: July 20 17:30-17:45

Linking maar eruptions with diatremes: experimental insights from single and multiple
buried explosions
Pierre-Simon Ross1 , James D.L. White2 , Greg A. Valentine3 , Jacopo Taddeucci4 , Ingo Sonder3 , Robin
G. Andrews2
1Centre Eau Terre Environnement, Institut national de la recherche scientifique (INRS), Canada,Geology Department, University of Otago, New Zealand, 3 Department of Geology and Center for
Geohazards Studies, University at Buffalo, USA, 4 Istituto Nazionale di Geofisica e Vulcanologia (INGV),Italy
2E-mail: rossps@ete.inrs.ca

Maar-diatreme eruptions are hazardous to people and infrastructure; kimberlitic diatremes can also containdiamonds so they are economically important. Yet processes occurring in the subsurface diatreme and theirrelation to surface eruptions are not yet well understood. Previous laboratory studies have addressed different
types of potential ’diatreme-forming’ processes, whereas previous field-scale experimental studies have addressed
cratering but without significant focus on sub-crater deposits, and only for single explosions. We conducted
field-scale experiments at the Geohazards Field Station (University at Buffalo, NY) using single and multiple buried
chemical explosions in a prepared, layered granular substrate. The explosions produced craters, extra-crater
deposits and sub-crater deposits analogous to volcanic maar craters, tephra rings and incipient diatremes.

We excavated a series of vertical cross-sections through the deposits after the explosions. This revealed asignificant zone of sub-crater deposits, extending several decimeters below the post-shot craters. Videos of theexperiments show vertical ejection and fallback of material, especially for the explosions that occurred below
optimal depth of burial. In other words, the majority of the material which formed these eruptive plumes fell backdirectly into the transient explosion craters. The sub-crater deposits have an upper zone containing domains
sourced from different substrate depths, and an underlying zone distinguished primarily by being more loosely
packed than the original substrate. We infer that much of the loosely packed material was disassembled, verticallytransported to different heights during the explosions, then fell back without significant relative lateral movement ofgrains. One explosion ejected material from the deepest substrate horizon, but it was redeposited only within thecrater and is unrepresented in the ejecta ring.

Implications of the experiments for maar-diatreme volcanoes are as follows: (1) vertical focusing of deep
explosions in the diatreme explains the deficit of deep wallrock lithics observed at maar volcanoes; (2) direct
vertical fallback is possibly a major process forming diatreme deposits; (3) direct fallback from numerous explosions
at various depths and lateral positions would eventually produce a diatreme fill that looks "well mixed" overall; (4)even in our limited simulation the number and scaled depth of explosions clearly affect diatreme size and structure.
While representing a pilot study, these initial results already advance our understanding of explosive cratering andhave implications for understanding how some features of maar-diatreme volcanoes and some kimberlite pipesform.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

849