A comparatively rectilinear conglomeration of ice fragments formed by pressure at the contact line between icefloes, usually along earlier existing cracks and leads or at the boundary between ice floes of different age. In this case, isostatically unbalanced hummocks usually form on the older ice surface. Ice ridges can also form as a result of direct fracturing of ice fields of thick and even first-year and multiyear ice at very strong pressures. The underwater portion of a ridge is termed an ice keel.
For the last two seasons down here I’ve volunteered to take groups out on the sea ice pressure ridges in front of the New Zealand research station, Scott Base. I went out about once a week for month and it is incredible to see the slow, yet rapid, changes that occur as the days get longer and the temperatures higher.