acquired October 23, 2021
Sri Lanka’s Granite Fortress
- Landsat 8 - OLI
- Data Date: October 23, 2021
- Visualization Date: March 4, 2022
acquired December 1, 2008
Two billion years ago, the piece of land that now makes up north central Sri Lanka had several active volcanoes. Though most of these ancient features have been worn away, their remnants persist in the form of towering pillars of rock that soar above the surrounding plain.
Two of these features—geologists call them inselbergs—are visible in the satellite image shown above. The tower of rock that appears in the center of the image, Sigiriya, has sheer cliffs that rise as high as 180 meters (600 feet) above the surrounding landscape.
Fifth-century king Kasyapa had a palace and fortress built on Sigirya’s relatively flat summit, along with a protective moat and an expansive water garden at the base. With as many as one million visitors each year, Sigiryia is one of Sri Lanka’s best-known historical sites. It was declared a UNESCO World Heritage Site in 1982. The photograph above shows the inselberg seen from the water garden. The photograph below shows ruins on the summit.
acquired February 24, 2022
About a kilometer to the north is Pidurangala, a geologically similar feature. When Kasyapa built his palace on Sigiryia, the Buddhist monks who had been living there were relocated to Pidurangala. The temple complex at Pidurangala remains today and includes a series of caves filled with ancient Buddhist sculptures and paintings.
Both of these inselbergs were likely volcanic plugs, funnel-shaped hunks of igneous rock that formed within volcanic vents. The plugs (or necks) are made of hardened magma that crystallized into erosion-resistant granite or other igneous rocks. The plugs separated large magma chambers below and vents at the surface.
The Operational Land Imager (OLI) on Landsat 8 acquired the image shown at the top of the page on October 23, 2021.
- BBC (2021, December 6) Sigiriya: Sri Lanka’s ancient water gardens. Accessed March 4, 2022.
- Cooray, J. (2012) The Sigiriya Royal Gardens. Analysis of the Landscape Architectonic Composition. Architecture and the Built Environment, 6.
- The Globe and Mail (2017, March 30) In the heart of the old country. Accessed March 4, 2022.
- Kathupotha, J. (2014) Diversity of vegetation types of the Pidurangala Granitic Inselberg, near Sigiriya, Sri Lanka: a Preliminary Study. Accessed March 4, 2022.
- Migon, P. (2021) Granite Landscapes, Geodiversity and Geoheritage—Global Context. Heritage, 4 (1), 198-219.
- Sigiriya Fortress (2022) Sigiriya Lion Rock. Accessed March 4, 2022.
- TrishansOz (2021) How Sigiriya was Formed. Accessed March 4, 2022.
- UNESCO (1982) Ancient City of Sigiriya. Accessed March 4, 2022.
NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. First photograph of the Sigiriya inselberg by Claire Rowland. Photograph of summit ruins and text by Adam Voiland.
This image record originally appeared on the Earth Observatory. Click here to view the full, original record.