Walker | first = George P.L. | coauthors = Edgardo Cañón-Tapia, & Emilio Herrero-Bervera
  | title = Birkettin basalttivirtauksen �Kolumbianjoen ylätasanko� vesikkelien kerrostumisen ja kaksinkertaisen imbrikaation alkuperä endogeenisen kasvun avulla | journal = Journal of Volcanology and Geothermal Research | volume = 88 | issue = | pages = 15-28 | publisher = | date = 1999 | url = | jstor = | issn = | doi = | id = | accessdate = 28 August 2011 }} 
{{Cite journal | last =