It looks like there's been a new development following North Korea's earlier threats.
New photo shows work at NKorea nuclear test site - Yahoo! NewsWASHINGTON (AP) — New satellite imagery appears to show a train of mining carts and other preparations under way at North Korea's nuclear test site but no indication of when a detonation might take place.
Early this month, South Korean intelligence reported digging of a new tunnel at the Punggye-ri site, which it took as a sign that North Korea was covertly preparing for a third nuclear test.
So photos gathered between March 8 and April 18 and provided by the Associated Press were analyzed at the John Hopkins School of Advanced International Studies.
Over 8,000 cubic meters of rubble has been excavated. I think they're a bit serious.