They form when lava accumulates within cracks in lava, superheats and explodes in a steam explosion, breaking the rock apart and depositing it on the volcanos flank. Consecutive explosions of this type eventually generate the cone.Volcanoes known to have Surtseyan activity include:

Surtsey, Iceland. The volcano built itself up from depth and emerged above the Atlantic Ocean off the coast of Iceland in 1963. Initial hydrovolcanics were highly explosive, but as the volcano grew, rising lava interacted less with water and more with air, until finally Surtseyan activity waned and became more Strombolian. Ukinrek Maars in Alaska, 1977, and Capelinhos in the Azores, 1957, both examples of above-water Surtseyan activity. Mount Tarawera in New Zealand erupted along a rift zone in 1886, killing 150 people. Ferdinandea, a seamount in the Mediterranean Sea, breached sea level in July 1831 and caused a sovereignty dispute between Italy, France, and Great Britain. The volcano did not build tuff cones strong enough to withstand erosion and soon disappeared back below the waves. The underwater volcano Hunga Tonga in Tonga breached sea level in 2009. Both of its vents exhibited Surtseyan activity for much of the time. It was also the site of an earlier eruption in May 1988. Submarine
Submarine eruptions occur underwater.
This has led to some controversy about the ability of physical examination tests to accurately diagnose between bursitis, impingement, impingement with or without rotator cuff tear and impingement with partial versus complete tears. In 2005, Park et al. published their findings which concluded that a combination of clinical tests were more useful than a single physical examination test. For the diagnosis of impingement disease, the best combination of tests were "any degree (of) a positive Hawkins–Kennedy test, a positive painful arc sign, and weakness in external rotation with the arm at the side", to diagnose a full thickness rotator cuff tear, the best combination of tests, when all three are positive, were the painful arc, the drop-arm sign, and weakness in external rotation. Signs and symptoms
Subacromial bursitis often presents with a constellation of symptoms called impingement syndrome. Pain along the front and side of the shoulder is the most common symptom and may cause weakness and stiffness. If the pain resolves and weakness persists other causes should be evaluated such as a tear of the rotator cuff or a neurological problem arising from the neck or entrapment of the suprascapular nerve. The onset of pain may be sudden or gradual and may or may not be related to trauma. Night time pain, especially sleeping on the affected shoulder, is often reported. Localized redness or swelling are less common and suggest an infected subacromial bursa.