Hawaiian volcanoes tend to erupt basalt, which is low in viscosity and low in gas content (about 0.5 weight percent). The gas that is present can readily escape and little pressure builds up in the magma. At the other extreme, rhyolite magmas are very viscous and can contain a lot of gas (up to 7-8 weight present).
The Japanese tree lilac, Syringa reticulata, grows 20 to 30 feet tall with a spread of 15 to 25 feet forming an oval-to round-shaped small tree. The large panicles of fragrant white flowers appear in early to mid-June. 'Ivory Silk,' 'Chantilly Lace,' 'Regent' and 'Summer Snow' are good cultivars.
Large Shrubs. The common lilac (Syringa vulgaris) is the largest shrub species of the plant when it comes to height and spread. They can reach up to 20 feet tall and wide. Native to Eastern Europe, their flowers are shades of pink or blue. It takes five years after planting for them to begin producing flowers.