The Greenstone Flow

Lava flow

Cross-section of the Lake Superior basin showing the tilted strata of volcanic rock that form Isle Royale. The Greenstone Flow forms the main ridge at Isle Royal.[1]

The Greenstone Flow is one of the world's largest known lava flows, estimated at a volume ~1650 to ~6000 cubic kilometers of mafic lava.[2][3] In places, the lava pooled to depth of 487 meters.[4] The flow was generated by a flood basalt eruption during the Midcontinental Rift, which occurred 1.1 billion years ago.[5] Where the cooled lava is exposed, it forms much of the Keweenaw Peninsula and Isle Royal in Lake Superior. At Isle Royal, the flow forms the backbone of the island and the Greenstone Ridge trail runs along its length.[1] The flow is the typical source for the semiprecious Isle Royale greenstone.[6]

## References

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1. ^ a b "USGS: Geological Survey Professional Paper 754—C (The Portage Lake Volcanics on Isle Royale)". www.nps.gov. Retrieved 2024-10-28.
2. ^ "Large Lava Flows". geo.mtu.edu. Retrieved 2024-10-23.
3. ^ Zhang, Yiming; Swanson‐Hysell, Nicholas L.; Schmitz, Mark D.; Miller, James D.; Avery, Margaret S. (13 September 2021). "Synchronous Emplacement of the Anorthosite Xenolith‐Bearing Beaver River Diabase and One of the Largest Lava Flows on Earth". Geochemistry, Geophysics, Geosystems. 22 (10). doi:10.1029/2021GC009909. ISSN 1525-2027.
4. ^ "How to explore a billion-year-old volcanic mystery along Lake Superior". Travel. 2024-10-23. Retrieved 2024-10-23.
5. ^ "Lake Superior Geology (U.S. National Park Service)". www.nps.gov. Retrieved 2024-10-23.
6. ^ "Exploring the Rich History of Michigan's Greenstone". www.mainstreetrocks.com. Retrieved 2024-10-28.