Diamonds have been revered as precious stones for over 2000 years, yet they are composed simply of carbon, one of the most common elements on Earth. Their rarity arises from the fact that they form at extreme pressures deep in the Earth’s mantle and then are brought rapidly to the surface in CO2-rich explosive eruptions. No such eruptions have occurred in human history, but we know they occur only in the interiors of continents, where they produce narrow vertical ‘kimberlite pipes’ that are mined in Africa, Russia, and, more recently, Canada. Tiny diamonds with a completely different origin have been found in meteorites, and some of these appear to predate the formation of our solar system. Nowadays, diamonds can also be grown artificially; these synthetic crystals are widely used in industry and, increasingly, in jewelry. For geologists, diamonds are invaluable tools for understanding the Earth’s interior. They are used to make tiny “anvils” that allow us to conduct high-pressure laboratory experiments that replicate conditions deep inside the Earth, and they commonly contain minute inclusions of other minerals that are our only actual samples of mantle materials from depths as great as ~400 km (250 miles). In this talk Jeff will provide how and where diamonds form, offer a brief summary of how we search for them, describe their history as gemstones, and detail what they tell us about our planet’s deep interior.
This IN-PERSON ONLY lecture will start at 4 PM on Saturday, February 15, 2025. This event is free and open to the public. (Donations gratefully welcome at the door.) The lecture will be recorded and posted shortly after the presentation, as are all our events since 2020.
ABOUT THE SPEAKER:
Jeff Tepper was on faculty of the Geology Department at the University of Puget Sound from 2001-2021 and has been emeritus since then. He earned his PhD from UW, where he studied the origins of granite in the North Cascades. At UPS he taught classes in mineralogy, petrology, geochemistry, GIS, and geomythology. Most of his research projects focus on the magmatic and tectonic history of the Pacific Northwest (including Tomanowas Rock) or on the geochemistry of water and sediment from Tacoma-area lakes. Visit Jeff’s website for more information: https://www.jeffreytepper.com/.
Cold War Science and Engineering Today Reveals Greenland’s Fragility in an Overheating Climate
Greenland, a remote arctic island, holds in its ice enough water to raise sea level over six meters (20 feet). That is enough to flood every major coastal city and displace up to half a billion people. Yet, until recently we knew very little about the past comings and goings of this massive ice sheet. Through the lens of climate science, environmental history, and the stories of people who studied Greenland over the past century, Paul will use the past to look into a warming future. He will fill the talk with photographs, movies, and recordings from the 1930s onward, review the science done by the international team that he led, and tell stories from his book, When the Ice is Gone. A key finding of Paul and his fellow researchers is that the Greenland ice sheet appears to have melted away completely during a previous interglacial warm climate, which suggests it could do so again if today’s warmer climate continues. The talk will be accessible to anyone with an interest in science and history.
A small preview to Paul’s lecture may be found at:
Paul Bierman, environmental science professor at the University of Vermont, develops methods to date ice and rocks. He has published in Science and Nature, with the findings covered by CNN, USA Today, and the Weather Channel. Paul is a 1993 graduate of the University of Washington (Seattle) where he earned his MS and doctorate in Geoscience after a BA at Williams College.
Paul lives in Burlington, Vermont and his passions include telling stories and solving the mysteries of our planet. He is equally at home in a dusty archive and a cleanroom without a speck of dust. A history and geoscience researcher by training and a teacher for over four decades, Paul looks at our planet with wonder and curiosity. His career has taken him to searing deserts and frigid ice sheets. Throughout, he has focused his energies on understanding the link between our Earth and human societies – what today we call, sustainability. He enjoys education at all levels and is the author of three textbooks and a book for the general public, When the Ice is Gone.
The Lecture: What Happens When You Crash Iceland into North America? A view of Washington 50 million years ago…
The Puget Lowland of Washington State contains several potentially dangerous seismic faults, including the Seattle fault, which runs south of downtown Seattle. To accurately assess the earthquake hazard in this region, we need to understand the architecture and geologic history of the rocks that host these faults, deep below the Puget Lowland. Geologists do this by using small changes in Earth’s gravity and magnetic fields to create images of the Earth’s subsurface. These rocks formed in a subduction zone 50 million years ago when a set of volcanic islands, similar to modern-day Iceland, collided with the edge of North America. This added a mass of rock, called Siletzia, to the continent. Megan showed us that as the islands piled up, they broke and folded into mountain ranges. South of Seattle, Siletzia was pushed up and over ancient North America, whereas to the north, Siletzia was pulled down and under the continent. She argued that a tear in Siletzia between these two zones eventually became the proto-Seattle fault, which provides a story for the Seattle fault’s origin and earliest history. Her images provided information that can improve models of ground shaking from future earthquakes affecting the greater Seattle urban area. *AGU abstract below.
This was an in-person only lecture, 4 PM on Saturday, November 16, 2024.
* AGU article abstract: Deep Structure of Siletzia in the Puget Lowland: Imaging an Obducted Plateau and Accretionary Thrust Belt with Potential Fields
Detailed understanding of crustal components and tectonic history of forearcs is important due to their geological complexity and high seismic hazard. The principal component of the Cascadia forearc is Siletzia, a composite basaltic terrane of oceanic origin. Much is known about the lithology and age of the province. However, glacial sediments blanketing the Puget Lowland obscure its lateral extent and internal structure, hindering our ability to fully understand its tectonic history and its influence on modern deformation. In this study, we apply map-view interpretation and two-dimensional modeling of aeromagnetic and gravity data to the magnetically stratified Siletzia terrane revealing its internal structure and characterizing its eastern boundary. These analyses suggest the contact between Siletzia (Crescent Formation) and the Eocene accretionary prism trends northward under Lake Washington. North of Seattle, this boundary dips east where it crosses the Kingston arch, whereas south of Seattle the contact dips west where it crosses the Seattle uplift (SU). This westward dip is opposite the dip of the Eocene subduction interface, implying obduction of Siletzia upper crust at this southern location. Elongate pairs of high and low magnetic anomalies over the SU suggest imbrication of steeply-dipping, deeply rooted slices of Crescent Formation within Siletzia. We hypothesize these features result from duplication of Crescent Formation in an accretionary fold-thrust belt during the Eocene. The active Seattle fault divides this Eocene fold-thrust belt into two zones with different structural trends and opposite frontal ramp dips, suggesting the Seattle fault may have originated as a tear fault during accretion.
About the Speaker:
Megan Anderson is an earthquake geophysicist at the Washington Geological Survey. Megan spent her early years in Kent, WA, during which the eruption of Mt. St. Helens spurred her fascination with geology, which was her major at Carleton College in Minnesota. She studied subduction processes and earthquakes in South America for her Ph.D. at the University of Arizona. She has studied numerous tectonic regions of the world but has always made her way back to the Pacific Northwest because there is so much left to discover. She taught for ten years at Colorado College, dragging her students and equipment across the country to do research in Washington. She is now firmly planted in Olympia as home.
The Puget Lowland of Washington State contains several potentially dangerous seismic faults, including the Seattle fault, which runs south of downtown Seattle. To accurately assess the earthquake hazard in this region, we need to understand the architecture and geologic history of the rocks that host these faults, deep below the Puget Lowland. Geologists do this by using small changes in Earth’s gravity and magnetic fields to create images of the Earth’s subsurface. These rocks formed in a subduction zone 50 million years ago when a set of volcanic islands, similar to modern-day Iceland, collided with the edge of North America. This added a mass of rock, called Siletzia, to the continent. Megan showed us that as the islands piled up, they broke and folded into mountain ranges. South of Seattle, Siletzia was pushed up and over ancient North America, whereas to the north, Siletzia was pulled down and under the continent. She argued that a tear in Siletzia between these two zones eventually became the proto-Seattle fault, which provides a story for the Seattle fault’s origin and earliest history. Her images provided information that can improve models of ground shaking from future earthquakes affecting the greater Seattle urban area. *AGU abstract below.
Megan Anderson is an earthquake geophysicist at the Washington Geological Survey. Megan spent her early years in Kent, WA, during which the eruption of Mt. St. Helens spurred her fascination with geology, which was her major at Carleton College in Minnesota. She studied subduction processes and earthquakes in South America for her Ph.D. at the University of Arizona. She has studied numerous tectonic regions of the world but has always made her way back to the Pacific Northwest because there is so much left to discover. She taught for ten years at Colorado College, dragging her students and equipment across the country to do research in Washington. She is now firmly planted in Olympia as home.