In this paper, we present an automatic approach for facial expression recognition from 3D video sequences. In the proposed solution, the 3D faces are represented by collections of radial curves and a Riemannian shape analysis is applied to effectively quantify the deformations induced by the facial expressions, in a given subsequence of 3D frames. This is obtained from the \textit{Dense Scalar Field}, which denotes the shooting directions of the geodesic paths constructed between pairs of corresponding radial curves of two faces. As the resulting Dense Scalar Fields show a high dimensionality, LDA transformation is applied to the dense feature space. Two methods are then used for classification: (i) 3D motion extraction with temporal HMM modeling; and (ii) Mean deformation capturing with Random Forest. While a dynamic HMM on the features is trained in the first approach, the second one computes mean deformations under a window and applies multi-class Random Forest. Both of the proposed classification schemes on the scalar fields showed comparable results and outperformed earlier studies on facial expression recognition from 3D video sequences.