We study the Newton polygon jumping locus of a Mumford family
in char p. Our main result says that, under a mild assumption on p, the
jumping locus consists of only supersingular points and its cardinality is equal
to (p^r − 1)(g − 1), where r is the degree of the defining field of the base curve
of a Mumford family in char p and g is the genus of the curve. The underlying
technique is the p-adic Hodge theory.