When Þingvellir was declared a national park Iceland had still not achieved full independence from Denmark. In 1904 Iceland had been granted home rule and in 1918 Iceland became a sovereign state within the Danish Kingdom, with the Danish king as the head of state. When Iceland was declared a republic in 1944 it was done at Þingvellir.
The ceremony was held on June 17, the birthdate of Jón Sigurðsson, the 19th century leader of the Icelandic Independence movement.
Þingvellir is constantly expanding.
The entire Þingvellir region is located in a rift valley created by the drifting apart of the North American and Eurasian tectonic plates.
The tectonic plates are drifting in opposite direction at the rate of 2cm (0.8 in) annually.
The plate boundary runs through Iceland. In Reykjanes peninsula the plates inch past each other at a constant rate, but at Þingvellir, they move in opposite directions, breaking apart. This causes the land between them to subside.