Twitter is a social news service in which information is selected and distributed by individual members of the tweet audience. While communication literature has studied traditional news media and the propagation of information, to our knowledge there have been no studies of the new social media and their impacts on the propagation of news during extreme event situations. This exploration attempts to build an understanding of how preexisting hyperlink structures on the Web and different types of information channels affect Twitter audiences' information selection. The study analyzes the concentration of user-selected information sources in Twitter about the 2009 Israel-Gaza conflict. There are three findings. First, a statistical test of a power-law structure revealed that, while a wide range of information was selected and redistributed by Twitter users, the aggregation of these selections over-represented a small number of prominent websites. Second, binomial regression analyses showed that Twitter user selections were not constituted randomly but were affected by the number of hyperlinks received and the types of information channels. Third, temporal analyses revealed that sources via social media channels were more prominently selected especially in the later stages of the news information lifespan.