Geochemistry, Mineralogy, Petrology & Volcanology

How do crystal aggregates form in magma chambers?

EGU Guest blogger September 5, 2019

EBSD map of chromite crystals colored according to the orientation, showing random orientations.

By Penny Wieser (PhD student at the University of Cambridge) Clues into the inner workings of volcanoes can be gleamed from material which is erupted at the surface, or that which solidified at depth in the crust. Just before eruption, three main phases are present: a gas phase (containing water, carbon dioxide, sulphur, chlorine etc), a liquid melt phase (the magma), and a solid phase (consisting ...[Read More]

Fire, Fog, Frost, Famine – French Revolution? The Lakagígar eruption in Iceland, 1783-1784 [Part 2]

Will Hutchison May 22, 2018

Lava fountains of the fissure eruption in Holuhraun, northeast of Bárðarbunga (Iceland) in 2014. The fountains are about 70-90 meters in height. Image credit: Joschenbacher

PART II: Were the Haze Hardships caused by Men? Famine Before the Lakagígar eruption, the population of Iceland was 48810 people; four years later, it was down to 38518. Disregarding about 1500 deaths which were caused by a smallpox epidemic, the eruption may still have killed about 1/6 of the population [5]. These deaths were not directly caused by the lava or by toxic gases. The main cause was h ...[Read More]

Fire, Fog, Frost, Famine – French Revolution? The Lakagígar eruption in Iceland, 1783-1784 [Part 1]

Will Hutchison May 9, 2018

The southwestern part of the Lakagígar fissure, seen from the mountain Laki. The flat land to the left of the crater row is covered by rough ‘a’a-lava. The black stretches to the right are covered by tephra (solidified lava fragments) which was probably formed by violent interaction between rising magma and ground water. Photo credit: Claudia Wieners

“On the 8th of June 1783, at Whitsun, there gushed forth from the mountains behind the summer pastures a fire which devastated land, cattle and humans with its effects, both nearby and far away”, wrote Reverend Jón Steingrímsson of Kirkjubæjarklaustur in his autobiography [2]. The “fire” which welled up from a volcanic fissure now known as Lakagígar (the craters of Mount Laki) was the biggest floo ...[Read More]

Building a lava dome: one block at a time

Will Hutchison February 7, 2018

Lava domes form when lava is extruded from a volcanic vent, but is too viscous to flow far away. Think of thick treacle that does not flow as easily as runny honey, and so when it is extruded, it forms a “lava pile” around the vent. Lava domes commonly form within the crater of a larger volcano (e.g. Mt. St. Helens), but can also stand alone or form part of a “dome complex”. A lava dome can take o ...[Read More]