February 16, 2017

Lauren and the giant pumice

Posted by Lauren Lipuma

Conveners Karin Orth and Rebecca Carey from the University of Tasmania say googbye at the end of the meeting.

By Lauren Lipuma

Lauren Lipuma is AGU’s public information specialist. She attended the AGU Chapman Conference on submarine volcanism in Hobart, Tasmania from January 29 – February 3. Read previous blog posts from this trip here.

The submarine volcanism Chapman Conference is at an end, and by all means it was a success. We had 102 scientists from 13 countries, including 27 students, attend. Submarine volcanologists got to talk to subaerial volcanologists. We saw cool videos of scientists pouring lava over water and ice. We went on a field trip and saw seals and dolphins. We talked about lots and lots of volcanoes (I stopped counting at 27).

A lot of talk on Thursday was focused on “the giant pumice” from a July 2012 eruption of Havre Seamount (seamount = underwater volcano). Havre is located in the Kermadec arc – a volcanic island chain north of New Zealand formed by subduction of the Pacific Plate beneath the Australian Plate.

Havre’s 2012 eruption was unusual because it spewed a ridiculous (technical term) amount of pumice into the Pacific Ocean. A large amount of pumice settled on the seafloor after the eruption, but some of the super buoyant rock made it all the way to the sea surface where it formed a giant pumice raft that was initially 400 square kilometers (150 square miles) in area – about the size of Philadelphia. (Pumice fun fact: by October of 2012, pieces of the raft covered an area of ocean more than twice the size of New Zealand.)

The giant pumice raft viewed from space.
Credit: NASA Earth Observatory.

Researchers studying the Havre eruption are trying to find out why the eruption produced so much pumice and how it managed to produce a giant pumice raft when the seamount is located 700 meters (2,300 feet) below sea level (most pumice rafts form from eruptions less than 100 meters (330 feet) below sea level).

Some of the Chapman Conference attendees studied the 2012 Havre eruption and brought back a piece of the giant pumice that had settled on the seafloor. (They collected it from a research cruise in 2015). At the end of the meeting, I was lucky enough to see the giant pumice in the flesh. I visited the lab of Rebecca Carey, one of the conference conveners and a geologist at the University of Tasmania. Rebecca is part of the Havre research team and has a large chunk of the giant pumice she affectionately calls “precious.”

Grad student Sam Mitchell shows me the giant pumice, also known as precious.

After spending some time with the giant pumice (in a room entirely filled with rocks from the 2015 research cruise), Karin Orth, another of the conveners and geologist at UTas, showed me some other cool things on display in the geology department. I learned that rocks glow under UV light and saw how geologists identify different types of rock by examining how light passed through their crystals. There was even an old analog seismograph!

Adam Soule, Karin Orth and Ryan Portner show me around the geology department at UTas. This display is dedicated to Darwin, whom, I learned, was also a geologist.

This is what happens when you put rocks under a UV light.

Just some of the rocks collected during the Havre research cruise.

Karin shows me how geologists identify rocks under a microscope.

Karin makes some mounts to preserve and analyze bits of rock.

An old analog seismograph.

—Lauren Lipuma is AGU’s public information specialist. Follow her on twitter at @Tenacious_She and on Instagram at laurenthepuma.