## 1 Introduction  
Tsunamis are potentially deadly and destructive sea waves. Most of the tsunamis are formed as a result of submarine earthquakes and submarine landslides. These landslides, in turn, are often triggered by earthquakes or volcanic eruptions [1]. Over the past 20 years, catastrophic tsunamis in Papua New Guinea (1998), Indian Ocean (2004), Japan (2011), Palu Bay Indonesia (2018), and Anak Krakata Indonesia (2018) have driven major advances in understanding of earthquakes and submarine landslides as tsunami sources [2]. In fact, submarine landslides have become suspects in the creation of the \"silent tsunami\" triggered by distant earthquakes. As exemplified by the 2018 Anak Krakatau Tsunami event, the tsunamis were initiated away from the epicentral area of an associated earthquake, or were far larger than expected given the earthquake magnitude. The silent tsunamis arrived without precursory seismic warning. They were generated by a landslide caused by the Anak Krakatau volcanic eruption. A landslide-generated tsunami may occur independently or along with an earthquake-generated tsunami, which can complicate the warning process and increase the losses [3]. Although the landslide-generated waves characteristically have shorter periods than the observed tsunami waves, the combination of the waves is able to produce long waves comparable with those observed, due to the ringing effects of the trapped waves inside a bay or coastal area [4]. The landslide can be classified as block collapse (slides) and sediment or mud collapse (slumps). The difference between them is mainly in the rigidity of the sliding body. Slides are landslides with rigid sliding bodies, and slumps are landslides with deformable sliding bodies [5; 6; 7]. The special consideration regarding this particular condition is to model the slump kinematics, based on the forces acting on the slump and the rheology of the slump materials. This study aims to develop a slump-type landslide model for the future study on landslide-generated tsunamis. In order to reduce the complexity, this paper shall focus on the developing a model to describe the kinematics and dynamics of pure landslides. After the model validation and sensivity analyses, this model can be used to study the tsunamis generated by slumps. In terms of the pure landslide simulations, the failure of the gypsum tailings dam in East Texas in 1966 (FGT66) is one of the famous benchmark problems. FGT66 features a field-scale with a clean and simple geometry. In this study, the benchmark problem, FGT66, will be studied thoroughly to develop a reliable landslide model. Similar to the slump-type landslide tsunami, the tailings are considered a fine material by [PERSON] [8], [PERSON] [9], and [PERSON] [10]. Numerically, the slumps and tailings fluid can be considered a viscoplastic material with the yield stress, which is one of the important parameters. Mudflow can be modeled by Bingham model [11; 12; 13], Herschel-Bulkley model [14; 15], and the Coulomb-viscoplastic model [16] by incorporating them with the depth-integrated equations models. The viscosity in these models is discontinuous [17]. The analytical solution was first proposed by [PERSON] [18]. The behavior of tailings was described by the Bingham model (BM) [18]. A one-dimensional profile and a freezing time were provided [18]. [PERSON] [12] studied a spreading flow of high concentration mud on an inclined plane. An analytical solution to a thin sheet of Bingham fluid was derived and verified with experimental data [12]. [PERSON] [15] studied the spreading of a two-dimensional, unsteady mudflow on a steep slope. The nonlinear rheological properties of the mud were described by the Herschel-Bulkley model [15]. In their paper [15], the von Karman integral method was used to derive the depth-averaged continuity and momentum equations. The influences of shear-thinning on the free-surface profiles and spreading characteristics of the mudflow were discussed [15].