Cry Me a Pele’s Tear

Written by: Alexis Stansfield, Earth & Environmental Science, Lehigh University

Cover image: Hawaiian volcano erupting (Credit: U.S. National Park Service) 

Pele is the deity responsible for creating all 137 Hawaiian islands. She is the goddess of volcanoes and fire, as well as the goddess of life and death, since lava enriches Hawaiian soil but is also highly destructive. 

Every rock on these islands is considered one of Pele’s children, and taking anything from the islands is said to incur her wrath via a lifetime of bad luck. Sometimes, tiny droplets from a lava fountain solidify into glass beads known as “Pele’s tears” and long strands of volcanic glass can form what’s known as “Pele’s hair.” Pele’s tears preserve bubbles of gas and crystal shards from the lava, so their composition might tell us a lot about eruptions that happened long ago.

Mystery Crystals

Scott Moyer, a master’s student in Lehigh University’s Earth & Environmental Science program, is seeking to answer that question. Pele’s tears are not widely studied, and there is a wealth of new knowledge to gain from them. When Moyer was looking at these droplets under a microscope, he noticed the glass coating had come off of some of them, revealing interesting and unexpected structures inside the tears. He noticed thin crystals radiating out from a central point in the rock. Moyer is the first to propose that the unidentified structures inside Pele’s tears are spherulites, which form in some lavas during cooling.

To test his theory, he found that the crystals had lower iron concentrations than the surrounding volcanic glass, which confirmed that they are indeed spherulites. Moyer published his findings in May, 2023¹ (link). Interestingly, spherulites are usually found in lavas with a higher silicon content, such as the sticky, explosive lava from cone volcanoes like Mount St Helens, whereas the shield volcanoes of Hawaii are formed by flowing liquid lava made of basalt. They may be showing up in this case due to instability of the volcanic glass during cooling. This uneven cooling may create chemical “zones” in the lava droplet that allow the crystals to form. Confirming the cause would be an interesting topic for future research to explore. 

Pele’s tears (Photo Credit: J. D. Griggs / US Geological Survey)

Four slices of Pele’s tears, showing bubbles and crystals within the glassy structure. (Photo Credit: Scott Moyer²)

Lava Fountains

Moyer is also examining the bubbles within Pele’s tears. He is studying the mathematical relationships between the amount and size of bubbles in the tears, and the height of the lava fountain that formed those tears. These relationships come about because the amount of gas in a lava fountain directly influences how high the fountain reaches into the sky, and that gas forms bubbles in the cooled volcanic rocks.

The initial hypothesis proposed that greater gas presence in the lava would propel a high lava fountain, and that this plentiful gas would lead to large and abundant bubbles in Pele’s tears formed from the eruption. Contrary to this hypothesis, Moyer found that higher lava fountains with more gas produced Pele’s tears with smaller and fewer bubbles. This indicates that the gas was, hypothetically, used up in powering the fountain. Thus, less gas was left in the lava by the time Pele’s tears were formed. 

Scientists who study volcanoes could collect Pele’s tears from ancient eruptions and use the  equations characterized in Moyer’s masters thesis² to figure out how high a lava fountain was, even millions of years later. 

Understanding the dynamics of lava fountains, how they form and how big they get based on their gas content, is vital to determining possible damage that can occur in forested and populated areas surrounding volcanic eruptions. The height of a lava fountain determines how widespread its destruction can become by influencing the extent of lava flow and rock debris spread by the eruption. Moyer’s work provides an important foothold for scientists to continue characterizing the dynamics of additional types of eruptions, including how lava is cooled and preserved, and what we can learn from remnants such as Pele’s tears. This is valuable to increase our awareness and our ability to mitigate the impacts of these natural processes.

Reference

Moyer, S., & Sahagian, D. (2023). Cry me a Pele’s tear: new insights on the internal structures of Pele’s tears. Frontiers in Earth Science, 11, 1184027.

Moyer, S. J. (2023). Use of Pele’s Tears and Spheres as an Indicator of Lava Fountain Height in Hawaiian Volcanoes (Doctoral dissertation, Lehigh University).