The locations of volcanic islands may be controlled by thin or extending parts of the lithosphere over a partially molten asthenosphere [Anderson and Bass, 1984; Favela and Anderson, 2000>, by edge effects near the boundaries of thick cratonic lithosphere [Anderson, 1998>, or by narrow jets of hot mantle rising from deep within the mantle [Campbell and Griffiths, 1992; Morgan, 1971; Wilson, 1986>. Many hotspots are found on or near ridges, at lithospheric discontinuities, or in extensional environments, so high resolution seismic images are required to determine whether it is lithospheric structure, stresses in the lithosphere, or the deep mantle that is the controlling factor for the location of these volcanoes. In this study, we perform a simple experiment in which we use basic geometrical arguments to better understand the resolution of tomographic images of the upper 400 km of the mantle under Iceland. Our results indicate that a narrow, deep seated mantle plume is not required in order to explain the observed travel time delays in this region. Results of tomographic inversions are often viewed as unique; however, recent seismic studies of the Icelandic Hotspot have illustrated the non-unique nature of these models. ¿ 2000 American Geophysical Union