Basics of polymyalgia rheumatica. Polymyalgia rheumatica (PMR) is a disorder that causes stiffness and aching that begins in the neck, shoulder and hip areas. It is not known whether it is a disease of the joints muscles or arteries.However it is thought that inflammation in these areas leads to pain and stiffness.Incidence.olymyalgia rheumatica (PMR) is a disorder that causes stiffness and aching that begins in the neck, shoulder and hip areas. It is not known whether it is a disease of the joints muscles or arteries. However it is thought that inflammation in these areas leads to pain and stiffness. Incidence.
There are two main types of volcanic eruptions: Explosive and Nonexplosive eruptions.he types of volcanic eruptions are magmatic, phreatomagmatic, and phreatic. For a description of each type and different styles of each, refer to the link below.
Explosive Eruptions. A second category of volcanoes are those characterized by explosive eruptions. Explosive eruptions are common to volcanoes with very viscous lava and high amounts of gas under pressure.The viscosity, or stickiness, of the lava relates to the silica content.xplosive eruptions are common to volcanoes along the  Ring of Fire , a string of volcanoes extending from the northwest coast of the United States, up through the Aleutian Islands, and into Japan.