Seracs developing on some large glaciers can be a problem of how to calculate a convincing total ice volume. However, estimation of seracs' contribution requires knowledge of seracs' landform. It is found that seracs on the East Rongbuk Glacier exhibit fractal characteristics with the box dimension varying from 1.3 to 1.9 and the dimensionless interzone about 40～160 m. The upstream of the seracs zone has a larger fractal dimension than that of downstream zone, indicating that ice seracs will lose its complexity while being developed. A random mid-point displacement method is applied to model ice seracs' form. Through constructing a seracs' ablation model, the ablation ratio of a serac body can be calculated, and it is demonstrated that the overall ablation ratio in the seracs zone approaches to 50% and is independent on landform parameters. As a result, the ice volume of seracs can be estimated within few landform parameters (e.g. the length of ice seracs' zone and the height of ice seracs). The contribution of ice seracs to the total glacier-ice volume of the East Rongbuk Glacier is ～3.7%, which can be neglected.

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