We consider the Cauchy problem for the system ∂tui +
divz(g(|u|)ui)
= 0, i ∈ {1,…, k}, in m space
dimensions and with g ∈ C3. When
k ≥ 2 and m = 2, we show
a wide choice of g's for which the bounded variation (BV) norm
of admissible solutions can blow up, even when the initial data
have arbitrarily small oscillation and arbitrarily small total
variation, and are bounded away from the origin. When m ≥ 3,
we show that this occurs whenever g is not constant, that is,
unless the system reduces to k decoupled transport equations
with constant coefficients.