{
    "format_version": "1.13.0",
    "minecraft:partially_exposed_blob_feature": {
      "description": {
        "identifier": "minecraft:underwater_magma_feature"
      },
      "places_block": "minecraft:magma",
      "placement_radius_around_floor": 1,
      "placement_probability_per_valid_position": 0.5,
      "exposed_face": "up"
    }
  }