Thunder Spike

You summon a 5ft diameter, 10ft tall spike of metallic rock that bursts through the ground at a point of your choosing within sight.  Anything within the space the spear occupies must make a dexterity saving throw, or take 4d10 piercing damage and anything within 15ft radius of the spike must make a constitution saving throw or take 4d6 thunder damage.  The spike then remains in place for the next minute, having an AC of 19 and 10 hit points, and can be used as half cover.