Vertical shear is recognized today as a key component of the stress balance of ice shelves. However, the first ice shelf models were built on the neglect of vertical shear. Partly due to its historical treatment, it remains common to discuss vertical shear as though it were still considered negligible in ice shelf models. Here, we offer a historical perspective on the changing treatment of vertical shear over time, and we emphasize the term's non-negligibility in current ice shelf modeling. We illustrate our discussion in the simplest context of an analytic, isothermal, shallow-ice-shelf model.

Analytic models of floating ice shelves date back to at least 1957, when Johannes Weertman derived expressions for the tension and velocity gradients within a uniform-thickness ice shelf

Using a depth-averaged constitutive relation, expressions of this form permit the calculation of strain rates and velocities. Nearly 2 decades later,

In originally deriving the nonuniform-thickness model of Eq. (

The formulation of Thomas' model evolved with the development of the shallow-shelf approximation (SSA)

The SSA is built on the fundamental assumption that the thickness-to-length aspect ratio,

However, the inclusion of vertical shear stress in the present-day interpretation of Thomas' model may somewhat clash with intuition, not least because the vertical shear term does not actually appear anywhere in Eq. (

For example, in constructing the ice shelf model of

An ice shelf cross-section alongside a visual description of several geometric parameters commonly used to describe ice shelf dynamics.

The typical balance of momentum for a 2D ice shelf cross-section, in

In contrast to their approach and with asterisks denoting appropriately scaled parameters, Eq. (

Following the workflow presented in Sect. 5.2 of

In discussions of shallow-ice-shelf models, it is fairly common to hear vertical shear spoken of as “zero”, “neglected”, or otherwise unimportant. While this certainly was an approximation made by early ice shelf modelers, this language is at odds with current modeling practice. Indeed, as first shown by

No data sets were used in this article.

CM devised the project and wrote the manuscript, with guidance from TCB and EME. TCB and EME both reviewed and edited the manuscript and acquired the financial support necessary for the project. TCB directly supervised CM.

The contact author has declared that none of the authors has any competing interests.

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This work was made possible by grant nos. 1716865 and 1933105 from the US National Science Foundation and grant no. 80NSSC18K1477 from NASA.

This research has been supported by the National Science Foundation (grant nos. 1716865 and 1933105) and the National Aeronautics and Space Administration (grant no. 80NSSC18K1477).

This paper was edited by Reinhard Drews and reviewed by four anonymous referees.